fix issue with resetting abm token teams

[ghernandez345]

For #24040

Add gitops option for the request to modify the app config.

There was an issue with the abm token teams getting reset to default anytime the PATCH /fleet/config endpoint was called. @jahzielv and I discussed various options on how to solve this and agreed that the approach taken in this PR was the quickest but not the best. Ideally, we'd like the gitops client to send back the data to the endpoint that its going to update. This will allow the PATCH /fleet/config endpoint to work like a standard PATCH request and only update the options provided instead of updating the app config differently depending on the client calling the endpoint.

• Changes file added for user-visible changes in changes/, orbit/changes/ or ee/fleetd-chrome/changes.
  See Changes files for more information.
• Added/updated automated tests
• Manual QA for all new/changed functionality

[codecov]

Codecov Report

Attention: Patch coverage is 76.92308% with 3 lines in your changes missing coverage. Please review.

Project coverage is 63.78%. Comparing base (b703e2e) to head (1d6ee73).
Report is 26 commits behind head on main.

Files with missing lines	Patch %	Lines
server/service/appconfig.go	66.66%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #26259      +/-   ##
==========================================
- Coverage   63.78%   63.78%   -0.01%     
==========================================
  Files        1653     1655       +2     
  Lines      158729   158962     +233     
  Branches     4093     4093              
==========================================
+ Hits       101253   101392     +139     
- Misses      49542    49624      +82     
- Partials     7934     7946      +12     

Flag	Coverage Δ
backend	64.61% <76.92%> (-0.01%)	⬇️

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[getvictor]

I'm sorry, I still don't understand the issue. In the code, it looks like you're checking newAppConfig.MDM.AppleBusinessManager.Set and newAppConfig.MDM.AppleBusinessManager.Value, which should be sufficient for PATCH.

It seems like you should just check newAppConfig.MDM.AppleBusinessManager.Set and do the following:

1. No one sets anything -- leave as is.

{
  "mdm": { /* empty */ }
}

2. Everything is cleared

{
  "mdm": {
    "apple_business_manager": null
  }
}

or

{
  "mdm": {
    "apple_business_manager": []
  }
}

I don't see the need for the new GitOps query option.

fleetctl gitops must always set something (null or array) for mdm.apple_business_manager

So, gitops should look at existing teams and set this array to match existing teams. Then, after teams have been processed (if new teams have been added), gitops can come back and patch this endpoint with the added teams. (I'm just speculating how this could work since I don't know the exact interactions.)

[mna]

It's missing the new tests, I think I'm too early to review?