feat: Repository-wide RunnerDeployment Autoscaling (#57)

* feat: Repository-wide RunnerDeployment Autoscaling

This adds `maxReplicas` and `minReplicas` to the RunnerDeploymentSpec. If and only if both fields are set, the controller computes and sets desired `replicas` automatically depending on the demand.

The number of demanded runner replicas is computed by `queued workflow runs + in_progress workflow runs` for the repository. The support for organizational runners is not included.

Ref https://github.com/summerwind/actions-runner-controller/issues/10

github/github.go

@@ -27,8 +27,10 @@ func NewClient(appID, installationID int64, privateKeyPath string) (*Client, err
 		return nil, fmt.Errorf("authentication failed: %v", err)
 	}
 
+	gh := github.NewClient(&http.Client{Transport: tr})
+
 	return &Client{
-		Client:    github.NewClient(&http.Client{Transport: tr}),
+		Client:    gh,
 		regTokens: map[string]*github.RegistrationToken{},
 		mu:        sync.Mutex{},
 	}, nil