Migrate to Docusaurus (#329)

* docs: initial migration to docusaurus

* website: add custom font, update blurbs and icons

* website: update splash

* root: update links to docs

* flows: use .pbflow extension so docusaurus doesn't mangle the files

* e2e: workaround prospector

* Squashed commit of the following:

commit 1248585dca
Author: Jens Langhammer <jens.langhammer@beryju.org>
Date:   Sun Nov 15 20:46:53 2020 +0100

    e2e: attempt to fix prospector error again

commit 1319c480c4
Author: Jens Langhammer <jens.langhammer@beryju.org>
Date:   Sun Nov 15 20:41:35 2020 +0100

    ci: install previous python version for upgrade testing

* web: update accent colours and format

* website: format markdown files

* website: fix colours for text

* website: switch to temporary accent colour to improve readability

* flows: fix path for TestTransferDocs

* flows: fix formatting of tests

website/docs/integrations/services/sentry/index.md

@@ -0,0 +1,48 @@
+---
+title: Sentry
+---
+
+## What is Sentry
+
+From https://sentry.io
+
+:::note
+Sentry provides self-hosted and cloud-based error monitoring that helps all software
+teams discover, triage, and prioritize errors in real-time.
+
+One million developers at over fifty thousand companies already ship
+better software faster with Sentry. Won’t you join them?
+:::
+
+## Preparation
+
+The following placeholders will be used:
+
+-   `sentry.company` is the FQDN of the Sentry install.
+-   `passbook.company` is the FQDN of the passbook install.
+
+Create an application in passbook. Create a SAML Provider with the following values
+
+-   ACS URL: `https://sentry.company/saml/acs/<sentry organisation name>/`
+-   Audience: `https://sentry.company/saml/metadata/<sentry organisation name>/`
+-   Issuer: `passbook`
+-   Service Provider Binding: `Post`
+-   Property Mapping: Select all Autogenerated Mappings
+
+## Sentry
+
+**This guide assumes you've installed Sentry using [getsentry/onpremise](https://github.com/getsentry/onpremise)**
+
+Navigate to Settings -> Auth, and click on Configure next to SAML2
+
+![](./auth.png)
+
+In passbook, get the Metadata URL by right-clicking `Download Metadata` and selecting Copy Link Address, and paste that URL into Sentry.
+
+On the next screen, input these Values
+
+IdP User ID: `urn:oid:0.9.2342.19200300.100.1.1`
+User Email: `urn:oid:0.9.2342.19200300.100.1.3`
+First Name: `urn:oid:2.5.4.3`
+
+After confirming, Sentry will authenticate with passbook, and you should be redirected back to a page confirming your settings.