refactor(git): Delegate commit function to platform (#13823)

lib/config/types.ts

lib/platform/commit.ts

lib/platform/types.ts

lib/util/git/types.ts

lib/workers/branch/__snapshots__/commit.spec.ts.snap

lib/workers/branch/commit.spec.ts

lib/workers/branch/commit.ts

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

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

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

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