add push flag to indicate target it GHAE

Signed-off-by: Florian Wagner <h2floh@github.com>

README.md

@@ -96,6 +96,8 @@ When no machine has access to both the public internet and the GHES instance:
    Limit push to specific repositories in the cache directory.
 - `actions-admin-user` _(optional)_
    The name of the Actions admin user, which will be used for updating the chosen action. To use the default user, pass `actions-admin`. If not set, the impersonation is disabled. Note that `site_admin` scope is required in the token for the impersonation to work.
+- `destination-is-ghae` _(optional)_
+   Indicates if the destination applicance is GHAE.
 
 **Example Usage:**
 

src/push.go

@@ -43,7 +43,7 @@ func (f *PushOnlyFlags) Init(cmd *cobra.Command) {
 	cmd.Flags().StringVar(&f.ActionsAdminUser, "actions-admin-user", "", "A user to impersonate for the push requests. To use the default name, pass 'actions-admin'. Note that the site_admin scope in the token is required for the impersonation to work.")
 	cmd.Flags().StringVar(&f.Token, "destination-token", "", "Token to access API on GHES instance")
 	cmd.Flags().BoolVar(&f.DisableGitAuth, "disable-push-git-auth", false, "Disables git authentication whilst pushing")
-	f.IsAE = false
+	cmd.Flags().BoolVar(&f.IsAE, "destination-is-ghae", false, "Destination instance is GHAE")
 }
 
 func (f *PushFlags) Validate() Validations {