github installation callback missing the "code" parameter

[motatoes]

in some cases github when an app installation is being updated it decides to not send a code paramter which we expect to recieve here:

digger/backend/controllers/github.go

Lines 1297 to 1305 in 1e88db8

	func (d DiggerController) GithubAppCallbackPage(c *gin.Context) {
	installationId := c.Request.URL.Query()["installation_id"][0]
	//setupAction := c.Request.URL.Query()["setup_action"][0]
	code := c.Request.URL.Query()["code"][0]
	appId := c.Request.URL.Query().Get("state")
	clientId, clientSecret, _, _, err := d.GithubClientProvider.FetchCredentials(appId)
	if err != nil {
	log.Printf("could not fetch credentials for the app: %v", err)

this causes an exception on callback and we need to handle it properly. The callback from github sometimes look like this: /github/callback?installation_id=1234567890&setup_action=update

In this case we need to handle a missing code parameter and then lookup the installation_id from the db records then perform the update accordingly somehow TBD