feat: add ci-test-examples

[NotAwar]

Fixes open-telemetry#454

Changes

• create a worfklow for testing the examples
• add bazel test to test everything under /examples
• add cmake test to test everything under /examples

Please provide a brief description of the changes here.

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

[marcalff]

Just found this branch today (by accident).

This work is not visible to opentelemetry-cpp maintainers and approvers.

To contribute to opentelemetry-cpp, PR must be done against the opentelemetry-cpp repository, not locally in a fork.

[NotAwar]

@marcalff at some point i started working on this to get it solved, but i never got it quite working so I ended up not making a pr.