Add tools/publish_wiki.py and the Publish wiki workflow, which make the
Gitea wiki equal wiki/ through the wiki REST API when a change to wiki/ is
merged to main. It needs its own secret TOKEN_FOR_GITEA_WIKI, refuses an
empty source and checks that the English pages are current first.
Document the secret in the credentials and troubleshooting guides and
regenerate the affected wiki pages.
Task: MIL-005#8
Tirsvad