tests(e2e): Refactor various tests

Goals:

- speedup
- less flakiness
- best practices and more use
- documentation

config:
- sync ports in Makefile and playwright config
  (otherwise, some tests fail locally because they assert the full URL including the (wrong) port)
- even more generous timeouts
- limit workers to one again (because I finally understand how
  Playwright works)
- allow nested functions to group them together with the related test

all:

- deprecate waitForLoadState('networkidle')
  - it is discouraged as per https://playwright.dev/docs/api/class-page#page-wait-for-load-state
  - I could not find a usage that seems to require it actually (see
    added documentation in README)
  - adding an exception should be made explicitly
  - it does not do what you might expect anyway in most cases
- only log in when necessary

webauthn:

- verify that login is possible after disabling key
- otherwise, the cleanup was not necessary after the previous refactor to create a fresh user each

issue-sidebar / WIP toggle:

- split into smaller chunks
- restore original state first
- add missed assertion to fix race condition (not waiting
  before state was reached)
- explicitly toggle the state to detect mismatch earlier

issue-sidebar / labels:

- restore original state first
- better waiting for background request

Makefile

@@ -716,7 +716,6 @@ test-e2e-pgsql\#%: playwright e2e.pgsql.test generate-ini-pgsql
 
 .PHONY: test-e2e-debugserver
 test-e2e-debugserver: e2e.sqlite.test generate-ini-sqlite
-	sed -i s/3003/3000/g tests/sqlite.ini
 	GITEA_ROOT="$(CURDIR)" GITEA_CONF=tests/sqlite.ini ./e2e.sqlite.test -test.run TestDebugserver -test.timeout 24h
 
 .PHONY: bench-sqlite