refactor(instr-undici): avoid use of deprecated APIs for diagnostic channels

[david-luna]

Which problem is this PR solving?

undici instrumentation is used deprecated APIs to subscribe to and unsubscribe from diagnostic channels. Eventually these APIs will be removed and the instrumentation won't work with newer versions of Node.js. I've considered to classify it as a fix but the deprecated APIs are still present so I think refactor is better.

Short description of the changes

• use new diagnostics_channel.subscribe(name, handler) and diagnostics_channel.unsubscribe(name, handler) APIs if available and fallback to diagnostics_channel.channel(name) if not

NOTE: this PR supersedes #2407

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.07%. Comparing base (dfb2dff) to head (ffa450a).
Report is 254 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2457      +/-   ##
==========================================
+ Coverage   90.97%   97.07%   +6.09%     
==========================================
  Files         146        8     -138     
  Lines        7492      410    -7082     
  Branches     1502       67    -1435     
==========================================
- Hits         6816      398    -6418     
+ Misses        676       12     -664     

see 138 files with indirect coverage changes

[david-luna]

@trentm thanks for the review. I've applied your suggestions myself so it's only necessary your approval (not sure of the approve settings in this repo)