Switch v1 collector pipeline to v2 Writer

[yurishkuro]

Which problem is this PR solving?

• Part of Use OTEL exporterhelper to implement a 2nd queue in v1 collector for OTLP data #6487
• Part of Optimizing the write path for mixed storage v1/v2 state #6474

Description of the changes

• Swap v1 spanWriter for v2 traceWriter in collector pipeline
• Currently the traceWriter is provided via v1 adapter, so it's always v1 writer underneath
• And since only v1 spans entry point is currently implemented, there is no performance impact from additional data transformations
• However, as soon as OTLP entry point is utilized (e.g. via OTLP receiver), the ptrace.Traces batch will be handled via exporterhelp queue as a single item (not broken into individual spans) and then passed directly to the writer as a batch. Since the writer is implemented via adapter the batch will be converted to spans and written one span at a time. There will be no additional data transformations on this path either.

How was this change tested?

• CI

Outstanding

• Invoking proper preprocessing, like sanitizers and collector tags, on the OTLP path
• Adequate metrics parity, ideally same as v1 collector
• Test coverage, including passing a v2-like (mock) writer that cannot be downgraded to v1
  • Idea: parameterize some tests (ideally those that also validate pre-processing) to execute both v1 and v2 write paths

[codecov]

Codecov Report

Attention: Patch coverage is 79.76190% with 17 lines in your changes missing coverage. Please review.

Project coverage is 96.22%. Comparing base (10af185) to head (98be3d7).

Files with missing lines	Patch %	Lines
cmd/collector/app/span_processor.go	84.00%	8 Missing and 4 partials ⚠️
storage_v2/v1adapter/writer.go	16.66%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6491      +/-   ##
==========================================
- Coverage   96.25%   96.22%   -0.04%     
==========================================
  Files         372      372              
  Lines       21282    21347      +65     
==========================================
+ Hits        20485    20541      +56     
- Misses        609      616       +7     
- Partials      188      190       +2     

Flag	Coverage Δ
badger_v1	10.65% <16.66%> (-0.03%)	⬇️
badger_v2	2.78% <0.00%> (-0.01%)	⬇️
cassandra-4.x-v1-manual	16.54% <16.66%> (-0.03%)	⬇️
cassandra-4.x-v2-auto	2.71% <0.00%> (-0.01%)	⬇️
cassandra-4.x-v2-manual	2.71% <0.00%> (-0.01%)	⬇️
cassandra-5.x-v1-manual	16.54% <16.66%> (-0.03%)	⬇️
cassandra-5.x-v2-auto	2.71% <0.00%> (-0.01%)	⬇️
cassandra-5.x-v2-manual	2.71% <0.00%> (-0.01%)	⬇️
elasticsearch-6.x-v1	20.20% <16.66%> (-0.04%)	⬇️
elasticsearch-7.x-v1	20.27% <16.66%> (-0.03%)	⬇️
elasticsearch-8.x-v1	20.44% <16.66%> (-0.03%)	⬇️
elasticsearch-8.x-v2	2.77% <0.00%> (-0.01%)	⬇️
grpc_v1	12.29% <16.66%> (-0.03%)	⬇️
grpc_v2	9.09% <0.00%> (-0.01%)	⬇️
kafka-3.x-v1	10.33% <16.66%> (-0.03%)	⬇️
kafka-3.x-v2	2.78% <0.00%> (-0.01%)	⬇️
memory_v2	2.78% <0.00%> (+<0.01%)	⬆️
opensearch-1.x-v1	20.33% <16.66%> (-0.03%)	⬇️
opensearch-2.x-v1	20.32% <16.66%> (-0.03%)	⬇️
opensearch-2.x-v2	2.78% <0.00%> (+<0.01%)	⬆️
tailsampling-processor	0.51% <0.00%> (-0.01%)	⬇️
unittests	95.10% <79.76%> (-0.03%)	⬇️

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