refactor: extract commit analyzer

cmd/semantic-release/main.go

pkg/analyzer/commit/commit.go

pkg/analyzer/commit/commit_test.go

pkg/provider/github/github.go

pkg/provider/github/github_test.go

pkg/provider/gitlab/gitlab.go

pkg/provider/gitlab/gitlab_test.go

pkg/provider/repository.go

pkg/semrel/commit.go