HCA: Move ca variable logic to db table

[MagnusHJensen]

fixes: #31168

Checklist for submitter

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

Testing

• Added/updated automated tests

• QA'd all new/changed functionality manually

[codecov]

Codecov Report

❌ Patch coverage is 74.46809% with 24 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (feat-hydrant-ca@a040d77). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
server/fleet/certificate_authorities.go	77.27%	9 Missing and 1 partial ⚠️
server/service/apple_mdm.go	79.31%	4 Missing and 2 partials ⚠️
server/datastore/mysql/certificate_authorities.go	50.00%	2 Missing and 1 partial ⚠️
server/service/mdm.go	50.00%	2 Missing and 1 partial ⚠️
ee/server/service/scep_proxy.go	66.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@                Coverage Diff                 @@
##             feat-hydrant-ca   #31959   +/-   ##
==================================================
  Coverage                   ?   63.83%           
==================================================
  Files                      ?     1971           
  Lines                      ?   193297           
  Branches                   ?     6358           
==================================================
  Hits                       ?   123389           
  Misses                     ?    60241           
  Partials                   ?     9667           

Flag	Coverage Δ
backend	65.18% <74.46%> (?)

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[gillespi314]

Looks good!