[chore] Add naming conventions for signal-specific types

[evan-bradley]

Description:

Add rules in CONTRIBUTING.md that describe how to name types and functions that apply to a specific signal.

Link to tracking Issue:

Resolves #7050

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.05 🎉

Comparison is base (08985c4) 90.84% compared to head (7718e8d) 90.90%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7273      +/-   ##
==========================================
+ Coverage   90.84%   90.90%   +0.05%     
==========================================
  Files         293      293              
  Lines       14295    14077     -218     
==========================================
- Hits        12986    12796     -190     
+ Misses       1041     1013      -28     
  Partials      268      268              

Impacted Files	Coverage Δ
service/pipelines.go	90.00% <0.00%> (-6.13%)	⬇️
pdata/pmetric/generated_exemplarslice.go	100.00% <0.00%> (ø)
...porter/exporterhelper/internal/persistent_queue.go	100.00% <0.00%> (ø)
confmap/resolver.go	96.75% <0.00%> (+0.01%)	⬆️
service/service.go	68.03% <0.00%> (+0.09%)	⬆️
service/graph.go	98.67% <0.00%> (+0.43%)	⬆️
service/zpages.go	70.58% <0.00%> (+1.17%)	⬆️
featuregate/registry.go	95.58% <0.00%> (+24.93%)	⬆️

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