Adds configuration instructions for GAR integration settings

Context

The implementation is based on the design discussed in #439371 (comment 1791646691).

Design: #434384[Inactive.png]

What does this MR do

Adds configuration instructions for GAR integration settings.

Adds form title & max width to form inputs.

Deviation from design

The design shows the command in the a multiline code block however I found already existing implementation (code-instruction.vue) with the copy button. This is inline with other examples in the package registry.

Is now inline with design & uses multiline code block

Copy command

This discussion above mentions having the copy command be in sync with the Google project ID in the form but this is not possible with the current implementation of the integrations form. This needs deeper changes to be made to expose the current form state.

This now uses a placeholder.

MR acceptance checklist

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Screenshots or screen recordings

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Before	After

Previous version

Description	Screenshot
Before
After
Integration inactive
Integration active
Integration active accordion expanded

How to set up and validate locally

1. Enable container registry in the gdk https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/howto/registry.md#set-up-container-registry-to-display-in-ui-only

2. Simulate a SAAS instance in local GDK

3. In rails console enable the experiments

   Feature.enable(:gcp_artifact_registry)
   Feature.enable(:google_cloud_workload_identity_federation)

4. Visit Project > Settings > Integrations > Google Cloud Artifact registry

5. Confirm that the Configure Google Cloud IAM policies is visible & the accordion is expanded.

6. Add values to the form & click Save changes

7. Confirm that the Configure Google Cloud IAM policies is visible & the accordion is collapsed.

8. Confirm that link to personal access tokens takes user to /-/user_settings/personal_access_tokens link in a new tab

Related to #439371 (closed)