Repositories: v13 UserService.GetAllInGroup fix

[piers-taylor-1994]

Prerequisites

• I have added steps to test this contribution in the description below
  Fixes issue UserService.GetAllInGroup fails when there are a lot of users in the group #18420 for v13

Description

• Issue is fixed in v16.4/17 but still persists in v13 as referenced in original issue UserService.GetAllInGroup fails when there are a lot of users in the group #18420 (comment)
• Applied FetchByGroups() extension method like before to batch queries

Steps to reproduce

• Clone and deploy from v13 branch
• Have/create 6000+ users
• Add them all to the same group
• Call userService.GetAllInGroup( groupId ) manually in code to see exception (I quickly created a new Controller endpoint and manually called it from Postman)

Before

After

[github-actions]

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[AndyButland]

Thanks again @piers-taylor-1994 - we'll include this for the next 13 release too.