chore: remove panics from rm initialization

[amandavialva01]

Description

Remove panics from resource manager initialization and replace them with error messages so that it is easier to trace back and handle errors.

Test Plan

CI passes.

Checklist

• Changes have been manually QA'd
• User-facing API changes need the "User-facing API Change" label.
• Release notes should be added as a separate file under docs/release-notes/.
  See Release Note for details.
• Licenses should be included for new code which was copied and/or modified from any external code.

Ticket

DET-9975

[codecov]

Codecov Report

Attention: Patch coverage is 12.50000% with 21 lines in your changes are missing coverage. Please review.

Project coverage is 47.50%. Comparing base (4ae0987) to head (f4b204b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8983      +/-   ##
==========================================
+ Coverage   47.49%   47.50%   +0.01%     
==========================================
  Files        1167     1167              
  Lines      176285   176292       +7     
  Branches     2352     2352              
==========================================
+ Hits        83732    83755      +23     
+ Misses      92395    92379      -16     
  Partials      158      158              

Flag	Coverage Δ
backend	42.64% <12.50%> (+0.05%)	⬆️
harness	64.01% <ø> (-0.01%)	⬇️
web	42.83% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...ster/internal/rm/agentrm/agent_resource_manager.go	47.22% <60.00%> (+0.85%)	⬆️
...nal/rm/kubernetesrm/kubernetes_resource_manager.go	20.60% <0.00%> (ø)
master/internal/core.go	2.16% <0.00%> (-0.02%)	⬇️

... and 3 files with indirect coverage changes

[netlify]

✅ Deploy Preview for determined-ui canceled.

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[stoksc]

lgtm