OTLP metrics gRPC exporter

[paivagustavo]

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 #1991 (5a425da) into main (64b640c) will decrease coverage by 3.1%.
The diff coverage is 51.7%.

@@           Coverage Diff           @@
##            main   #1991     +/-   ##
=======================================
- Coverage   75.3%   72.1%   -3.2%     
=======================================
  Files        143     159     +16     
  Lines       6896    7954   +1058     
=======================================
+ Hits        5194    5742    +548     
- Misses      1495    1983    +488     
- Partials     207     229     +22     

Impacted Files	Coverage Δ
.../otlp/otlpmetric/internal/otlpmetrictest/client.go	0.0% <0.0%> (ø)
...lp/otlpmetric/internal/otlpmetrictest/collector.go	0.0% <0.0%> (ø)
...rs/otlp/otlpmetric/internal/otlpmetrictest/data.go	0.0% <0.0%> (ø)
...tlp/otlpmetric/internal/otlpmetrictest/otlptest.go	0.0% <0.0%> (ø)
...porters/otlp/otlpmetric/otlpmetricgrpc/exporter.go	0.0% <0.0%> (ø)
.../otlp/otlpmetric/internal/connection/connection.go	2.3% <2.3%> (ø)
...porters/otlp/otlpmetric/internal/otlpconfig/tls.go	40.0% <40.0%> (ø)
exporters/otlp/otlpmetric/exporter.go	55.2% <55.2%> (ø)
...ers/otlp/otlpmetric/internal/otlpconfig/options.go	72.5% <72.5%> (ø)
...otlp/otlpmetric/internal/metrictransform/metric.go	72.9% <72.9%> (ø)
... and 22 more