Add goleak check to cmd/agent/app/configmanager

[yurishkuro]

Which problem is this PR solving?

• Part of Enable and enforce goroutine leak checks in tests #5006

Description of the changes

• Add goleak check
• Call Stop on the factory for clean shutdown
• Run each test via t.Run so that defer runs in scope

cc @akagami-harsh

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7b42cf7) 95.60% compared to head (64ffd12) 95.60%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5015   +/-   ##
=======================================
  Coverage   95.60%   95.60%           
=======================================
  Files         319      319           
  Lines       18786    18786           
=======================================
  Hits        17960    17960           
  Misses        663      663           
  Partials      163      163           

Flag	Coverage Δ
cassandra-3.x	25.63% <ø> (ø)
cassandra-4.x	25.63% <ø> (ø)
elasticsearch-5.x	19.90% <ø> (ø)
elasticsearch-6.x	19.90% <ø> (+0.01%)	⬆️
elasticsearch-7.x	20.02% <ø> (-0.02%)	⬇️
elasticsearch-8.x	20.13% <ø> (+0.01%)	⬆️
grpc-badger	19.52% <ø> (ø)
kafka	14.12% <ø> (ø)
opensearch-1.x	20.04% <ø> (+0.01%)	⬆️
opensearch-2.x	20.02% <ø> (-0.02%)	⬇️
unittests	93.34% <ø> (ø)

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