Add HTTP metrics exporter for OTLP

[hanyuancheung]

Resolved: #2014 this is part of the #1827 todo list:

• add gRPC otlp trace exporter
• add gRPC otlp metrics exporter
• add HTTP otlp trace exporter
• add HTTP otlp metrics exporter
• refactor out the duplicated code (transform, connection, otlpconfig)
• update examples and remove old otlp gRPC/HTTP exporter
• update docs

[codecov]

Codecov Report

Merging #2022 (4bee63f) into main (d6e8f60) will increase coverage by 0.2%.
The diff coverage is 88.2%.

@@           Coverage Diff           @@
##            main   #2022     +/-   ##
=======================================
+ Coverage   72.4%   72.7%   +0.2%     
=======================================
  Files        161     164      +3     
  Lines       7943    8079    +136     
=======================================
+ Hits        5756    5876    +120     
- Misses      1961    1974     +13     
- Partials     226     229      +3     

Impacted Files	Coverage Δ
...ers/otlp/otlpmetric/internal/otlpconfig/options.go	64.9% <0.0%> (-7.7%)	⬇️
...porters/otlp/otlpmetric/otlpmetrichttp/exporter.go	0.0% <0.0%> (ø)
exporters/otlp/otlpmetric/otlpmetrichttp/client.go	93.2% <93.2%> (ø)
...xporters/otlp/otlpmetric/otlpmetrichttp/options.go	100.0% <100.0%> (ø)

[hanyuancheung]

Hi, all checks have passed, could anyone convenient help to review this PR? Thx.

[paivagustavo]

Thanks for taking this @zhyChesterCheung. Some small comments but overall looks good!

[hanyuancheung]

The problems mentioned above all have been fixed ~ @MrAlias @paivagustavo

[MrAlias]

@zhyChesterCheung can you merge in main and resolve the existing conflicts? This PR still needs another approval from an approver before it can be merged, but having it ready to merge will speed that up once it happens.

[hanyuancheung]

@zhyChesterCheung can you merge in main and resolve the existing conflicts? This PR still needs another approval from an approver before it can be merged, but having it ready to merge will speed that up once it happens.

All conflicts have been resolved, great to see the checks all passed and this PR is ready to merge. Could you merge it please? @MrAlias @paivagustavo