Enable user headers in the reflect call in client.connect

[lirao]

What?

Add a parameter reflectMetadata in client.connect to add user-provided headers in the reflect call.

Why?

Some GRPC servers require a header to authenticate any call (including reflection). The invoke command covers this use case, but the reflect command that's bundled in the connect command does not, which leads to authentication errors.

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (make ci-like-lint) and all checks pass.
• I have run tests locally (make tests) and all tests pass.
• I have commented on my code, particularly in hard-to-understand areas.

Related PR(s)/Issue(s)

Closes #3241

[CLAassistant]

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[codecov-commenter]

Codecov Report

Merging #3242 (f416f1f) into master (7184786) will decrease coverage by 0.06%.
The diff coverage is 66.66%.

❗ Current head f416f1f differs from pull request most recent head da66ac8. Consider uploading reports for the commit da66ac8 to get more accurate results

@@            Coverage Diff             @@
##           master    #3242      +/-   ##
==========================================
- Coverage   73.21%   73.16%   -0.06%     
==========================================
  Files         259      257       -2     
  Lines       19899    19906       +7     
==========================================
- Hits        14569    14564       -5     
- Misses       4406     4412       +6     
- Partials      924      930       +6     

Flag	Coverage Δ
ubuntu	73.16% <66.66%> (+0.01%)	⬆️
windows	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
js/modules/k6/grpc/client.go	84.03% <66.66%> (-0.66%)	⬇️

... and 8 files with indirect coverage changes

[codebien]

Hey @lirao,
thanks for your contribution. 🙏 Can you please sign the CLA so we can accept your contribution?

[lirao]

Hey @lirao, thanks for your contribution. 🙏 Can you please sign the CLA so we can accept your contribution?

Hi, is it ok if someone on the k6 team make this change instead? I can't sign the CLA.

[lirao]

Closing since I can't sign the CLA. Can someone else make this change instead?