Cloud License - Render connectivity error

What does this MR do?

It adds and controls an alert that will show if the user submitted the activation form and the backend responded with CONNECTIVITY_ERROR error.

The alert will explain what happens to the user and how they might be able to resolve the problem through links to the docs.

Note:

The feature is behind an application setting that won't be enabled on staging/production until the whole project is ready to be shipped.

In order to test this locally, enable ApplicationSetting.current.update(cloud_license_enabled: true) from rails console.

The setting won't be enabled on GitLab.com until the whole project is ready to be published.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because the change is behind an application setting that won't be enabled until the whole project is ready to be published.
• Code review guidelines
• Style guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

Related to #327253