feat(opentelemetry-web): capture decodedBodySize / http.response_content_length

[johnbley]

Capture encodedBodySize from PerformanceResourceTiming (when available); report as http.response_content_length.

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ John Bley (3852bd0)

[codecov]

Codecov Report

Merging #1262 into master will increase coverage by 0.22%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1262      +/-   ##
==========================================
+ Coverage   92.86%   93.09%   +0.22%     
==========================================
  Files         126      133       +7     
  Lines        3364     3764     +400     
  Branches      688      761      +73     
==========================================
+ Hits         3124     3504     +380     
- Misses        240      260      +20     

Impacted Files	Coverage Δ
...entelemetry-semantic-conventions/src/trace/http.ts	0.00% <ø> (ø)
packages/opentelemetry-web/src/types.ts	100.00% <ø> (ø)
...telemetry-plugin-fetch/src/enums/AttributeNames.ts	100.00% <100.00%> (ø)
...ntelemetry-web/src/enums/PerformanceTimingNames.ts	100.00% <100.00%> (ø)
packages/opentelemetry-web/src/utils.ts	94.59% <100.00%> (+0.11%)	⬆️
...ry-plugin-xml-http-request/src/enums/EventNames.ts	100.00% <0.00%> (ø)
...kages/opentelemetry-exporter-collector/src/util.ts	100.00% <0.00%> (ø)
...porter-collector/src/CollectorTraceExporterBase.ts	94.87% <0.00%> (ø)
...ages/opentelemetry-exporter-collector/src/types.ts	100.00% <0.00%> (ø)
.../opentelemetry-exporter-collector/src/transform.ts	96.34% <0.00%> (ø)
... and 2 more

[obecny]

My my concern is naming.
With regards to the size itself there are also decodedBodySize and encodedBodySize. Having that in mind should we create another issue to add those too deciding about suitable name from
https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/semantic_conventions/http.md#common-attributes

[obecny]

lgtm