Remove scheme from OTLP endpoint before passing to gRPC

[ThomsonTan]

Fixes #986

Changes

According to https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/exporter.md, URI scheme like http or https are allowed in the OTLP endpoint, but causes problem in naming resolving in gRPC. This change removes the URI scheme for OTLP gRPC.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #988 (dfa0590) into main (530cb30) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #988   +/-   ##
=======================================
  Coverage   95.41%   95.41%           
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  Files         161      161           
  Lines        6833     6833           
=======================================
  Hits         6519     6519           
  Misses        314      314           

[lalitb]

Nit, we can also use UrlParser :

UrlParser url(options.endpoint);
if (url.success_) {
  grpc_target = url.host_ + ":" + url.port_;
}

This will validate that url is in correct format, and remove path and query_string if added ?