web: Replace calls to rootInterface()?.tenant? with a contextual this.tenant object (#7778)

* This commit abstracts access to the object `rootInterface()?.config?` into a single accessor,
`authentikConfig`, that can be mixed into any AKElement object that requires access to it.

Since access to `rootInterface()?.config?` is _universally_ used for a single (and repetitive)
boolean check, a separate accessor has been provided that converts all calls of the form:

``` javascript
rootInterface()?.config?.capabilities.includes(CapabilitiesEnum.CanImpersonate)
```

into:

``` javascript
this.can(CapabilitiesEnum.CanImpersonate)
```

It does this via a Mixin, `WithCapabilitiesConfig`, which understands that these calls only make
sense in the context of a running, fully configured authentik instance, and that their purpose is to
inform authentik components of a user’s capabilities. The latter is why I don’t feel uncomfortable
turning a function call into a method; we should make it explicit that this is a relationship
between components.

The mixin has a single single field, `[WCC.capabilitiesConfig]`, where its association with the
upper-level configuration is made. If that syntax looks peculiar to you, good! I’ve used an explict
unique symbol as the field name; it is inaccessable an innumerable in the object list. The debugger
shows it only as:

    Symbol(): {
        cacheTimeout: 300
        cacheTimeoutFlows: 300
        cacheTimeoutPolicies: 300
        cacheTimeoutReputation: 300
        capabilities: (5) ['can_save_media', 'can_geo_ip', 'can_impersonate', 'can_debug', 'is_enterprise']
    }

Since you can’t reference it by identity, you can’t write to it. Until every browser supports actual
private fields, this is the best we can do; it does guarantee that field name collisions are
impossible, which is a win.

The mixin takes a second optional boolean; setting this to true will cause any web component using
the mixin to automatically schedule a re-render if the capabilities list changes.

The mixin is also generic; despite the "...into a Lit-Context" in the title, the internals of the
Mixin can be replaced with anything so long as the signature of `.can()` is preserved.

Because this work builds off the work I did to give the Sidebar access to the configuration without
ad-hoc retrieval or prop-drilling, it wasn’t necessary to create a new context for it. That will be
necessary for the following:

TODO:

``` javascript
rootInterface()?.uiConfig;
rootInterface()?.tenant;
me();
```

* This commit abstracts access to the object `rootInterface()?.tenant?` into a single accessor,
`tenant`, that can be mixed into any AKElement object that requires access to it.

Like `WithCapabilitiesConfig` and `WithAuthentikConfig`, this one is named `WithTenantConfig`.

TODO:

``` javascript
rootInterface()?.uiConfig;
me();
```

* web: Added a README with a description of the applications' "mental model," essentially an architectural description.

* web: prettier did a thing

* web: prettier had opinions about the README

* web: Jens requested that subscription be  by default, and it's the right call.

* web: Jens requested that the default subscription state for contexts be , and it's the right call.

* web: prettier having opinions after merging with dependent branch

* web: prettier still having opinions.

web/src/elements/Interface/Interface.ts

@@ -1,6 +1,9 @@
 import { config, tenant } from "@goauthentik/common/api/config";
 import { UIConfig, uiConfig } from "@goauthentik/common/ui/config";
-import { authentikConfigContext } from "@goauthentik/elements/AuthentikContexts";
+import {
+    authentikConfigContext,
+    authentikTenantContext,
+} from "@goauthentik/elements/AuthentikContexts";
 import type { AdoptedStyleSheetsElement } from "@goauthentik/elements/types";
 import { ensureCSSStyleSheet } from "@goauthentik/elements/utils/ensureCSSStyleSheet";
 
@@ -21,9 +24,6 @@ type AkInterface = HTMLElement & {
 };
 
 export class Interface extends AKElement implements AkInterface {
-    @state()
-    tenant?: CurrentTenant;
-
     @state()
     uiConfig?: UIConfig;
 
@@ -45,6 +45,24 @@ export class Interface extends AKElement implements AkInterface {
         return this._config;
     }
 
+    _tenantContext = new ContextProvider(this, {
+        context: authentikTenantContext,
+        initialValue: undefined,
+    });
+
+    _tenant?: CurrentTenant;
+
+    @state()
+    set tenant(c: CurrentTenant) {
+        this._tenant = c;
+        this._tenantContext.setValue(c);
+        this.requestUpdate();
+    }
+
+    get tenant(): CurrentTenant | undefined {
+        return this._tenant;
+    }
+
     constructor() {
         super();
         document.adoptedStyleSheets = [...document.adoptedStyleSheets, ensureCSSStyleSheet(PFBase)];

web/src/elements/Interface/authentikConfigProvider.ts

@@ -12,7 +12,7 @@ export function WithAuthentikConfig<T extends Constructor<LitElement>>(
     superclass: T,
     subscribe = true,
 ) {
-    class WithAkConfigProvider extends superclass {
+    abstract class WithAkConfigProvider extends superclass {
         @consume({ context: authentikConfigContext, subscribe })
         public authentikConfig!: Config;
     }

web/src/elements/Interface/tenantProvider.ts

@@ -0,0 +1,20 @@
+import { authentikTenantContext } from "@goauthentik/elements/AuthentikContexts";
+
+import { consume } from "@lit-labs/context";
+import type { LitElement } from "lit";
+
+import type { CurrentTenant } from "@goauthentik/api";
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+type Constructor<T = object> = abstract new (...args: any[]) => T;
+
+export function WithTenantConfig<T extends Constructor<LitElement>>(
+    superclass: T,
+    subscribe = true,
+) {
+    abstract class WithTenantProvider extends superclass {
+        @consume({ context: authentikTenantContext, subscribe })
+        public tenant!: CurrentTenant;
+    }
+    return WithTenantProvider;
+}