Remove unused "namespace" field from Badger config

[yurishkuro]

Which problem is this PR solving?

• NamespaceConfig had a private namespace field which is not necessary
• Part of [jaeger-v2] Align Badger Storage Config With OTEL #5926

Description of the changes

• Remove the field, clean up the tests

How was this change tested?

• CI

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.82%. Comparing base (ad6af7a) to head (2a6e6fa).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5929      +/-   ##
==========================================
+ Coverage   96.81%   96.82%   +0.01%     
==========================================
  Files         344      344              
  Lines       16531    16530       -1     
==========================================
+ Hits        16004    16005       +1     
+ Misses        340      339       -1     
+ Partials      187      186       -1     

Flag	Coverage Δ
badger_v1	8.04% <11.11%> (-0.02%)	⬇️
badger_v2	1.82% <0.00%> (+<0.01%)	⬆️
cassandra-3.x-v1	16.61% <0.00%> (+<0.01%)	⬆️
cassandra-3.x-v2	1.75% <0.00%> (+<0.01%)	⬆️
cassandra-4.x-v1	16.61% <0.00%> (+<0.01%)	⬆️
cassandra-4.x-v2	1.75% <0.00%> (+<0.01%)	⬆️
elasticsearch-6.x-v1	18.79% <0.00%> (+<0.01%)	⬆️
elasticsearch-7.x-v1	18.85% <0.00%> (+0.01%)	⬆️
elasticsearch-8.x-v1	19.04% <0.00%> (+0.01%)	⬆️
elasticsearch-8.x-v2	1.81% <0.00%> (-0.02%)	⬇️
grpc_v1	9.49% <0.00%> (+0.01%)	⬆️
grpc_v2	7.15% <0.00%> (+<0.01%)	⬆️
kafka-v1	9.74% <0.00%> (+<0.01%)	⬆️
kafka-v2	1.82% <0.00%> (+<0.01%)	⬆️
memory_v2	1.82% <0.00%> (+<0.01%)	⬆️
opensearch-1.x-v1	18.89% <0.00%> (+0.01%)	⬆️
opensearch-2.x-v1	18.89% <0.00%> (+<0.01%)	⬆️
opensearch-2.x-v2	1.81% <0.00%> (+<0.01%)	⬆️
tailsampling-processor	0.46% <0.00%> (+<0.01%)	⬆️
unittests	95.30% <100.00%> (+0.01%)	⬆️

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