feat(core/onboarding): support manual rebase/retry (#17633)

docs/usage/self-hosted-configuration.md

lib/config/options/index.ts

lib/config/types.ts

lib/util/hasha.ts

lib/workers/repository/index.ts

lib/workers/repository/onboarding/branch/index.spec.ts

lib/workers/repository/onboarding/branch/index.ts

lib/workers/repository/onboarding/branch/rebase.spec.ts

lib/workers/repository/onboarding/branch/rebase.ts

lib/workers/repository/onboarding/common.ts

...repository/onboarding/pr/__snapshots__/index.spec.ts.snap

lib/workers/repository/onboarding/pr/index.spec.ts

lib/workers/repository/onboarding/pr/index.ts