core: Tidy contributor onboarding, fix typos. (#12700)

core: Tidy contributor onboarding.

- Fixes typos.
- Fixes stale links.
- Tidies Makefile so that Poetry env is optional for hygiene commands.
- Remove mismatched YAML naming.
- Uses shebang on Python scripts.
- Document semver usage.
- Redirect OpenAPI schema.

Signed-off-by: Teffen Ellis <592134+GirlBossRush@users.noreply.github.com>

scripts/generate_semver.py

@@ -0,0 +1,15 @@
+#!/usr/bin/env python3
+"""
+Generates a Semantic Versioning identifier, suffixed with a timestamp.
+"""
+
+from time import time
+
+from authentik import __version__ as package_version
+
+"""
+See: https://semver.org/#spec-item-9 (Pre-release spec)
+"""
+pre_release_timestamp = int(time())
+
+print(f"{package_version}-{pre_release_timestamp}")