Use bytes::Bytes as the HTTP request body in HttpClient.

[mstyura]

This will allow pooling of buffers on caller side compared to usage of Vec.

Fixes

Lack of possibility to reuse buffers which are consumed by HttpClient after request has been sent.

Design discussion issue

Should old function be kept with deprecated annotation and hence new function had to have a different name or should I just introduce breaking change by changing signature of a function?

Changes

I propose to change type of body of http request accepted by HttpClient trait from Vec<u8> to bytes::Bytes.
This should unblock pooling of buffers which can be used both for serialization & being http request bodies.
Something like this (pseudo-code to get the idea):

async fn export(&mut self, batch: Vec<SpanData>) -> ExportResult  {
    let mut buffer = pool.get();
    let request = self.build_request(&mut buffer, batch);
    let res = send_request(client, request);
    pool.return(buffer);
    res
}

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.

Project coverage is 77.9%. Comparing base (42b4f2f) to head (e0156e6).

Files with missing lines	Patch %	Lines
opentelemetry-http/src/lib.rs	0.0%	6 Missing ⚠️
opentelemetry-otlp/src/exporter/http/logs.rs	0.0%	2 Missing ⚠️
opentelemetry-otlp/src/exporter/http/metrics.rs	0.0%	2 Missing ⚠️
opentelemetry-otlp/src/exporter/http/trace.rs	0.0%	2 Missing ⚠️
opentelemetry-zipkin/src/exporter/uploader.rs	0.0%	2 Missing ⚠️
...try-sdk/src/trace/sampler/jaeger_remote/sampler.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #2485     +/-   ##
=======================================
- Coverage   77.9%   77.9%   -0.1%     
=======================================
  Files        123     123             
  Lines      22925   22928      +3     
=======================================
  Hits       17870   17870             
- Misses      5055    5058      +3     

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[mstyura]

Hello @cijothomas
Could you please take a look at this PR once you have time?
Thanks a lot in advance!