feat: use a modified batch span processor that creates metrics

[tim-mwangi]

Description

This is to track spans received and dropped by the processor. Currently the processor silently drops spans when the queue is full which is quite difficult to debug. There's a debug log but then this means the user modifying their code to enable it and the logs being quite noisy. Using metrics is much better.

Testing

Tested locally.

Checklist:

• [ ✅ ] My changes generate no new warnings
• [ ✅ ] I have added tests that prove my fix is effective or that my feature works

[codecov]

Codecov Report

Merging #201 (fe1ac96) into main (c886e58) will decrease coverage by 5.54%.
The diff coverage is 37.92%.

@@            Coverage Diff             @@
##             main     #201      +/-   ##
==========================================
- Coverage   64.99%   59.45%   -5.54%     
==========================================
  Files          49       53       +4     
  Lines        1774     2200     +426     
==========================================
+ Hits         1153     1308     +155     
- Misses        570      832     +262     
- Partials       51       60       +9     

Impacted Files	Coverage Δ
...nstrumentation/hypertrace/net/hyperhttp/handler.go	0.00% <0.00%> (ø)
...ntation/opentelemetry/batchspanprocessor/logger.go	0.00% <0.00%> (ø)
...atchspanprocessor/batch_span_processor.modified.go	20.14% <20.14%> (ø)
...n/opentelemetry/batchspanprocessor/env.modified.go	30.23% <30.23%> (ø)
instrumentation/opentelemetry/init_additional.go	79.10% <70.00%> (+1.32%)	⬆️
instrumentation/opentelemetry/init.go	81.12% <77.77%> (-1.39%)	⬇️
sdk/instrumentation/net/http/handler.go	28.69% <84.21%> (+2.84%)	⬆️
...nstrumentation/opencensus/net/hyperhttp/handler.go	100.00% <100.00%> (ø)
...ion/opentelemetry/batchspanprocessor/bspcreator.go	100.00% <100.00%> (ø)
...opentelemetry/github.com/gin-gonic/hypergin/gin.go	89.36% <100.00%> (+0.23%)	⬆️
... and 3 more

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