feat(instrumentation-http): Add API for adding custom metric attributes

[klippx]

Which problem is this PR solving?

Add a clear and intuitive API to configure custom metric attributes that a user may inject (unrelated to span context).

Fixes #4107
Related discussion: #4088

Short description of the changes

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

There are only two metrics recorded, they should both get the custom attributes:

• Unit test assertion: Ensure custom metric attributes are added to client http bucket
• Unit test assertion: Ensure custom metric attributes are added to server http bucket

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: klippx / name: Mathias Klippinge (01aa559, bc47738)

[legendecas]

Thank you for working on this!

[codecov]

Codecov Report

Merging #4108 (cc974d7) into main (73b4466) will decrease coverage by 1.78%.
The diff coverage is n/a.

❗ Current head cc974d7 differs from pull request most recent head bc47738. Consider uploading reports for the commit bc47738 to get more accurate results

@@            Coverage Diff             @@
##             main    #4108      +/-   ##
==========================================
- Coverage   92.31%   90.53%   -1.78%     
==========================================
  Files         330      159     -171     
  Lines        9417     3763    -5654     
  Branches     1993      838    -1155     
==========================================
- Hits         8693     3407    -5286     
+ Misses        724      356     -368     

see 182 files with indirect coverage changes

[klippx]

@legendecas does it look good to you now?

[klippx]

@legendecas Hi, can we merge this please? 🙏

[klippx]

👻

Guess I got ghosted, lets close this.

[naorpeled]

Hey @legendecas,
hope you're doing well!
sorry for bumping this.

How can I achieve this functionality with the current implementation of the library?

[alexa-gt]

@klippx @legendecas what happened here?

[alexa-gt]

Never mind me. I see the changes relate to static label values only and I was looking for a dynamic one.

[GraemeF]

I'd like to add the service name as an attribute on http metrics - seems like it isn't possible without something like this.

[klippx]

The marked answer has been updated to reflect how we solved this: #4088 (reply in thread)

This fixes the problem across all metrics, not only http metrics.