docs: add Container Registries usage documentation

[malta895]

Description

Pull Request Type

• Documentation content changes
• Bugfix / Missing Redirects
• Docusaurus site code changes

PR Checklist

• The commit message follows our guidelines included in the CONTRIBUTING.md
• All tests of Lint, cspell and check-content pass. (How to launch them?)
• No sensitive content has been committed

Other information

[malta895]

Suggested change

	If you need to use a container registry hostname that is not present in the dropdown list, you have to create it in the Project Settings, or contact your Project Administrator or Company Owner to do it for you.
	If you need to use a container registry hostname that is not present in the dropdown list, you have to create it in the Project Settings, or contact your Project Administrator or Company Owner to do it for you.
	In case a service already uses a container registry not in the list, a warning badge will advise the user to create it, or to choose a new one from the list. The project can still be saved with the unknown container registry, to avoid disruption.