feat(changelog): support gitea changelogs (#24144)

docs/usage/configuration-options.md

lib/constants/platforms.ts

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

lib/modules/platform/gitea/schema.ts

lib/util/common.spec.ts

lib/util/common.ts

lib/workers/repository/update/pr/changelog/api.ts

...orkers/repository/update/pr/changelog/gitea/index.spec.ts

lib/workers/repository/update/pr/changelog/gitea/index.ts

lib/workers/repository/update/pr/changelog/gitea/source.ts

lib/workers/repository/update/pr/changelog/release-notes.ts

lib/workers/repository/update/pr/changelog/source.ts

lib/workers/repository/update/pr/changelog/types.ts