Adding support for overriding grpc authority pseudo header

[ali-atac]

What?

Why?

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (make 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)

[CLAassistant]

All committers have signed the CLA.

[codebien]

Hey @ali-atac,
it seems a reasonable change as we already discussed in the past.
I see this pull request is in a draft state. However, as it hasn't changed for some days, let me clarify and remind you that signing the CLA is required to be able to merge your contribution.
I encourage you also to discuss before in a dedicated issue your proposal before spending relevant effort on it.

[codecov-commenter]

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (24ae4d9) 73.35% compared to head (96156bb) 73.28%.
Report is 5 commits behind head on master.

❗ Current head 96156bb differs from pull request most recent head d3fa362. Consider uploading reports for the commit d3fa362 to get more accurate results

Files	Patch %	Lines
js/modules/k6/grpc/client.go	12.50%	6 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3454      +/-   ##
==========================================
- Coverage   73.35%   73.28%   -0.08%     
==========================================
  Files         266      264       -2     
  Lines       19965    19968       +3     
==========================================
- Hits        14646    14633      -13     
- Misses       4409     4420      +11     
- Partials      910      915       +5     

Flag	Coverage Δ
ubuntu	73.28% <12.50%> (-0.03%)	⬇️
windows	?

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[mstoykov]

I would really prefer if we get a test about this.

Also this likely will conflict with #3152

[ali-atac]

Thanks for the comment, I'll add some tests next week

[codebien]

Hi @ali-atac,
#3152 has been merged, so you can now rebase to finalize the code. Are you still interested in working on it?

[codebien]

Hey!
I close this pull request because the offical doc mentions that authority is already a supported case for the dns:// resolver (the syntax is dns:[//authority/]host[:port]). If someone hits an issue with it, a specific bug report or a unit test is necessary before merging any dedicated logic for it.