add partial support for env var config to otlp/HTTP

[paivagustavo]

This PR adds partial supports for Environment Variables configurations on the otlp/HTTP driver.

What have I done:

• Added support for configuring Timeouts;
• Added support for configuring Endpoints, Headers, Compression and Timeout via Environment Variables;
• Split the http driver by signals (metrics and traces), making it possible to configure each individually;
• Simplified the struct of the otlphttp.Option creation, reducing the amount of non important code;

What is missing:

• Support for the tls certificate file, since the configuration of tls via env variables are different from the actual tls configuration, I postponed it to another PR otherwise this PR would be big;
• Support for environment variable configuration on the otlp/GRPC;

Part of #1085

[codecov]

Codecov Report

Merging #1758 (34182dd) into main (bf180d0) will increase coverage by 0.4%.
The diff coverage is 95.4%.

@@           Coverage Diff           @@
##            main   #1758     +/-   ##
=======================================
+ Coverage   78.2%   78.6%   +0.4%     
=======================================
  Files        132     133      +1     
  Lines       6948    7073    +125     
=======================================
+ Hits        5434    5561    +127     
+ Misses      1269    1267      -2     
  Partials     245     245             

Impacted Files	Coverage Δ
exporters/otlp/otlphttp/options.go	91.9% <91.9%> (+25.2%)	⬆️
exporters/otlp/otlphttp/envconfig.go	98.1% <98.1%> (ø)
exporters/otlp/otlphttp/driver.go	94.5% <100.0%> (+0.7%)	⬆️
exporters/trace/jaeger/reconnecting_udp_client.go	89.3% <0.0%> (-0.3%)	⬇️