Tweak MDM detection query to return the proper enrollment when there are multiple entries

[JordanMontgomery]

This change is deceptively simple but helps us choose the right one in cases like #29042 where there are multiple enrollments in the registry. In this case the customer seems to have been using something like co-management(though even using their MDM we have not repro'd internally) which leads to 2 registry keys in the registry with a UPN node. I believe the way some MDM services handle unenroll can also leave the registry keys in this state. Either way, because of this, and the fact that we have a LIMIT 1 in the query, we were, in 50% of the cases where we had multiple keys, returning the less useful of the nodes from the query and because no Server URL was coming back we were treating it as if the host was not MDM enrolled and thus, not unenrolling it, and leading to enrollment failing.

With this change we'll return the proper registry key which should allow us to, in the case of migration, properly unenroll the host and even in the case where a customer isn't using Fleet MDM will allow us to display the correct information from the registry.

Checklist for submitter

If some of the following don't apply, delete the relevant line.

• Changes file added for user-visible changes in changes/, orbit/changes/ or ee/fleetd-chrome/changes.
  See Changes files for more information.
• Input data is properly validated, SELECT * is avoided, SQL injection is prevented (using placeholders for values in statements)
• Manual QA for all new/changed functionality

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.26%. Comparing base (8b7a9a1) to head (c0841d0).
Report is 18 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #29360      +/-   ##
==========================================
- Coverage   64.27%   64.26%   -0.01%     
==========================================
  Files        1840     1840              
  Lines      179020   179020              
  Branches     5174     5174              
==========================================
- Hits       115059   115047      -12     
- Misses      54921    54929       +8     
- Partials     9040     9044       +4     

Flag	Coverage Δ
backend	65.25% <ø> (-0.01%)	⬇️

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[gillespi314]

LGTM!