testing: set pprof labels for goroutines that use the same code for different cases

[cce]

This sets a few profiler labels to identify a selection of goroutines used by algod. Since profiler data already lets you filter by function, we only need labels for cases where the same function is used by multiple goroutines for different cases. (E.g. low-prority worker pool vs high-priority worker pool; dedicated deserialization goroutines for different message types)

[codecov]

Codecov Report

Attention: Patch coverage is 91.30435% with 2 lines in your changes missing coverage. Please review.

Project coverage is 55.88%. Comparing base (d02ee6a) to head (4b9942f).

Files	Patch %	Lines
util/process.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4350   +/-   ##
=======================================
  Coverage   55.87%   55.88%           
=======================================
  Files         482      482           
  Lines       68571    68578    +7     
=======================================
+ Hits        38317    38325    +8     
+ Misses      27652    27650    -2     
- Partials     2602     2603    +1     

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[winder]

Neat. The docs on pprof.Do weren't really helpful for me, and I haven't spent a lot of time with profiling. It looks correct according to the blog post.

[jannotti]

How did you decide what to label? git grep "go.*()" and dig around? Or stuff you knew was interesting?

[algorandskiy]

@cce could you rebase it?

[algorandskiy]

I suggest not merging before p2p branch due to conflicts