Add stash provider bootstrap support

The new command set is:
  flux bootstrap bitbucket-server --owner=<project> --username=<user> --repository=<repository name> --hostname=<domain> --token-auth

There is a parity in the capabilities with the other providers.

Signed-off-by: Soule BA <soule@weave.works>

internal/bootstrap/provider/factory.go

@@ -22,6 +22,7 @@ import (
 	"github.com/fluxcd/go-git-providers/github"
 	"github.com/fluxcd/go-git-providers/gitlab"
 	"github.com/fluxcd/go-git-providers/gitprovider"
+	"github.com/fluxcd/go-git-providers/stash"
 )
 
 // BuildGitProvider builds a gitprovider.Client for the provided
@@ -51,6 +52,14 @@ func BuildGitProvider(config Config) (gitprovider.Client, error) {
 		if client, err = gitlab.NewClient(config.Token, "", opts...); err != nil {
 			return nil, err
 		}
+	case GitProviderStash:
+		opts := []gitprovider.ClientOption{}
+		if config.Hostname != "" {
+			opts = append(opts, gitprovider.WithDomain(config.Hostname))
+		}
+		if client, err = stash.NewStashClient(config.Username, config.Token, opts...); err != nil {
+			return nil, err
+		}
 	default:
 		return nil, fmt.Errorf("unsupported Git provider '%s'", config.Provider)
 	}

internal/bootstrap/provider/provider.go

@@ -22,6 +22,7 @@ type GitProvider string
 const (
 	GitProviderGitHub GitProvider = "github"
 	GitProviderGitLab GitProvider = "gitlab"
+	GitProviderStash  GitProvider = "stash"
 )
 
 // Config defines the configuration for connecting to a GitProvider.
@@ -33,6 +34,10 @@ type Config struct {
 	// e.g. github.example.com.
 	Hostname string
 
+	// Username contains the username used to authenticate with
+	// the Provider.
+	Username string
+
 	// Token contains the token used to authenticate with the
 	// Provider.
 	Token string