Adds custom form for GAR integration settings

What does this MR do and why?

Adds custom form for GAR integration settings

Adds new component under ee/integrations/edit/sections

Refactor the integration module to add sections

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Before	After
	When integration is active:

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 experiment

   Feature.enable(:gcp_artifact_registry)

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

5. Confirm that help text is visible & View artifacts button is not visible.

6. Confirm that when integration is activated, View artifacts button is visible & links to Project > Deploy > Google Artifact Registry

Related to #439371 (closed)