feat(datasource): add `gitea-tags` datasource (#24083)

lib/constants/platform.spec.ts

lib/constants/platforms.ts

lib/modules/datasource/api.ts

lib/modules/datasource/gitea-tags/index.spec.ts

lib/modules/datasource/gitea-tags/index.ts

lib/modules/datasource/gitea-tags/readme.md

lib/modules/datasource/gitea-tags/schema.ts

lib/util/http/auth.ts

lib/util/http/gitea.ts

lib/util/http/host-rules.spec.ts

lib/util/http/host-rules.ts