[adaptive sampling] Clean-up after previous refactoring

[yurishkuro]

Which problem is this PR solving?

• Previous refactoring left the code in a mixed up state

Description of the changes

• move provider / aggregator / post-aggregator into separate files named accordingly
• do the same for tests
• no actual code changes, just moving code around

How was this change tested?

• CI

[mahadzaryab1]

lgtm

[codecov]

Codecov Report

Attention: Patch coverage is 86.95652% with 9 lines in your changes missing coverage. Please review.

Project coverage is 96.80%. Comparing base (88a0319) to head (c3dcaac).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...gin/sampling/strategyprovider/adaptive/provider.go	86.95%	8 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5954       +/-   ##
===========================================
+ Coverage   51.44%   96.80%   +45.36%     
===========================================
  Files         176      345      +169     
  Lines        8869    16518     +7649     
===========================================
+ Hits         4563    15991    +11428     
+ Misses       3863      340     -3523     
+ Partials      443      187      -256     

Flag	Coverage Δ
badger_v1	8.03% <ø> (ø)
badger_v2	1.82% <ø> (ø)
cassandra-3.x-v1	16.62% <ø> (ø)
cassandra-3.x-v2	1.75% <ø> (ø)
cassandra-4.x-v1	16.62% <ø> (ø)
cassandra-4.x-v2	1.75% <ø> (ø)
elasticsearch-6.x-v1	18.79% <ø> (+0.01%)	⬆️
elasticsearch-7.x-v1	18.85% <ø> (ø)
elasticsearch-8.x-v1	19.03% <ø> (-0.02%)	⬇️
elasticsearch-8.x-v2	1.81% <ø> (ø)
grpc_v1	9.48% <ø> (-0.02%)	⬇️
grpc_v2	7.16% <ø> (ø)
kafka-v1	9.74% <ø> (ø)
kafka-v2	1.82% <ø> (ø)
memory_v2	1.82% <ø> (ø)
opensearch-1.x-v1	18.89% <ø> (-0.02%)	⬇️
opensearch-2.x-v1	18.90% <ø> (+0.01%)	⬆️
opensearch-2.x-v2	1.81% <ø> (ø)
tailsampling-processor	0.46% <ø> (ø)
unittests	95.28% <86.95%> (?)

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.