Jira Connect create branch page: Alert when lacking permissions

What does this MR do and why?

On the Jira Connect New Branch page, we add an alert when a user selects a project that don't have the push_code permission for.

Related to #337274 (closed)

Screenshots or screen recordings

demo_alert

How to set up and validate locally

1. On a given GitLab project, set your user permission such you don't have push_code permission for the project.

   Tip 👉 apply this diff to "force" set the pushCode permission to false for the Gitlab Test project.

diff --git a/app/assets/javascripts/jira_connect/branches/components/new_branch_form.vue b/app/assets/javascripts/jira_connect/branches/components/new_branch_form.vue
index 94cf4dd2748..2ab7e09c2f8 100644
--- a/app/assets/javascripts/jira_connect/branches/components/new_branch_form.vue
+++ b/app/assets/javascripts/jira_connect/branches/components/new_branch_form.vue
@@ -93,6 +93,9 @@ export default {
       this.selectedProject = project;
       this.selectedSourceBranchName = null; // reset branch selection
       this.hasPermission = this.selectedProject.userPermissions.pushCode;
+      if (this.selectedProject.name === 'Gitlab Test') {
+        this.hasPermission = false;
+      }
 
       if (!this.hasPermission) {
         this.setPermissionAlert();

1. Navigate to http://gdk.test:3000/-/jira_connect/branches/new
2. Select the project for which you don't have permission (if using the patch provided, select the Gitlab test project).
3. Observe. An alert should appear.
4. Select a different project. You should have push_code permission for this project.
5. Observe, the form should expand and no alert should appear.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.