Implement gitlab operations

[zeromsi]

Interface: https://github.com/klovercloud-ci-cd/integration-manager/blob/master/core/v1/service/git.go

type Git interface {
	GetPipeline(repositoryName, username, revision, token string) (*v1.Pipeline, error)
	GetDescriptors(repositoryName, username, revision, token, path, env string) ([]unstructured.Unstructured, error)
	GetDirectoryContents(repositoryName, username, revision, token, path string) ([]v1.GitDirectoryContent, error)
	CreateRepositoryWebhook(username, repositoryName, token string) (v1.GitWebhook, error)
	DeleteRepositoryWebhookById(username, repositoryName, webhookId, token string) error
}

Example: https://github.com/klovercloud-ci-cd/integration-manager/blob/master/core/v1/logic/github.go
https://gitlab.com/api/v4/users/username+/projects?search=repoName&access_token=
https://gitlab.com/api/v4/projects/repoId /hooks?access_token=