[TEST] Functional tests for OTLP/gRPC with mutual TLS

[chusitoo]

Fixes #2208

Changes

• There was only a main for http functional tests so a func_grpc_main was added following a similar pattern
• Add debug log line in OTLP grpc exporter to capture result in tests
• Reuse existing CI step "cmake_otprotocol_test" since it is the only one enabling WITH_OTLP_GRPC_SSL_MTLS_PREVIEW
• Minor tweaks to scripts to accommodate using both test binaries

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

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.16%. Comparing base (4998eb1) to head (9a21128).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3227   +/-   ##
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  Coverage   88.16%   88.16%           
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  Files         198      198           
  Lines        6224     6224           
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  Hits         5487     5487           
  Misses        737      737           

[chusitoo]

Because this script gets its inputs from run_test.sh and all other CI checks that run these tests only build WITH_OTLP_HTTP, I thought this would be the easiest solution to supporting existing checks that only test HTTP functionality as well this check that does gRPC, as well.

For visibility, this message is also shown as a notice in the annotations section:

[chusitoo]

Setting a timeout to speed things up a bit, since some tests might go on for 5+ seconds before erroring out.
The observable behavior is that a "deadline exceeded" will be output as a result instead of the actual reason. This is accounted for in expect_connection_failed().

If deemed more appropriate, it could be reverted so as to let the tests fail normally.

[chusitoo]

Reusing this test because it is the only one enabling WITH_OTLP_GRPC_SSL_MTLS_PREVIEW and also WITH_OTLP_GRPC so it sort of made sense to add functional tests to it

[marcalff]

LGTM, thanks for the tests.