Support default configs for storage backends

[yurishkuro]

Which problem is this PR solving?

• Many OTEL Collector components provide default configs such that users do not need to provide most settings.
• However, due to our organization of the storage extension config, there was no way to provide defaults

Description of the changes

• 🛑 breaking Change the main config inside out: instead of static separation by storage types followed by a map of custom names, move the map to the top level followed by static separation by storage type. E.g.

# before
    memory:
      some_storage:
        max_traces: 100000
# after
    backends:
      some_storage:
        memory:
          max_traces: 100000

• This required an introduction of an extra nesting via backends, which is a bit unfortunate, but the OTEL framework requires config to be a struct, it did not work with a map at the top level. Having a struct might actually be beneficial in the future if we need some top-level settings
• Add custom marshaling code where if a specific storage type is detected as set-by-user, then a default is created first (similar mechanism to how extension default configs is created by OTEL Collector, but unfortunately that mechanism is rigid, non-recursive)
• Change sample config files to the new format
• Use names some_store and another_store in configs to emphasize that those are custom names, not part of the config struct
• Add more unit tests for config

How was this change tested?

• Unit tests and CI

Checklist

• I have read https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md
• I have signed all commits
• I have added unit tests for the new functionality
• I have run lint and test steps successfully
  • for jaeger: make lint test
  • for jaeger-ui: yarn lint and yarn test

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.40%. Comparing base (9ba3238) to head (5a6a730).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5691      +/-   ##
==========================================
+ Coverage   96.38%   96.40%   +0.01%     
==========================================
  Files         334      334              
  Lines       16141    16144       +3     
==========================================
+ Hits        15558    15563       +5     
+ Misses        405      404       -1     
+ Partials      178      177       -1     

Flag	Coverage Δ
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cassandra-3.x-v1	16.63% <42.50%> (+0.03%)	⬆️
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elasticsearch-7.x-v1	18.86% <5.00%> (-0.01%)	⬇️
elasticsearch-8.x-v1	19.06% <5.00%> (-0.01%)	⬇️
elasticsearch-8.x-v2	19.06% <5.00%> (-0.03%)	⬇️
grpc_v1	9.45% <0.00%> (-0.03%)	⬇️
grpc_v2	7.39% <0.00%> (-0.09%)	⬇️
kafka	9.75% <0.00%> (-0.02%)	⬇️
opensearch-1.x-v1	18.90% <5.00%> (-0.03%)	⬇️
opensearch-2.x-v1	18.91% <5.00%> (-0.03%)	⬇️
opensearch-2.x-v2	18.91% <5.00%> (-0.03%)	⬇️
unittests	94.19% <90.81%> (-0.06%)	⬇️

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[yurishkuro]

@Wise-Wizard using your new lib here!

[Wise-Wizard]

🥳🥳🥳

[jkowall]

LGTM!