Fix policies to allow group maintainers/owners to see shared runners

What does this MR do and why?

Describe in detail what your merge request does and why.

Part of Shared instance runners are not visible to audi... (#376719 - closed)

This MR ensures that RunnerPolicy allows group maintainers/owners to see shared instance runners when Show only inherited toggle is off. In GraphQL: Add ALL_AVAILABLE membership value (!96770 - merged) only developers were allowed, due to a misunderstanding on my part regarding the API.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

In this screen, instance runners should be visible to a user that is an owner/maintainer/developer of a group that uses shared runners:

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Ensure you have an instance runner registered in http://gdk.test:3000/admin/runners

2. Navigate to http://gdk.test:3000/groups/gitlab-org/-/group_members (it is assumed that gitlab-org group has shared runners enabled in the Runners section of http://gdk.test:3000/groups/gitlab-org/-/settings/ci_cd - the default setting)

3. Change the Max role for Margeret Dare to Owner:

   

4. Click on the user name, and then click on the icon shown below:

   

5. Impersonate the user:

   

6. Navigate to http://gdk.test:3000/groups/gitlab-org/-/runners

7. Disable Show only inherited

8. Instance runner should be visible:

   branch	screenshot
   on this branch
   on master

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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