Name PubSubService tokio threads

[steviez]

Problem

These threads use the default name (tokio-runtime-worker). By not having specific names, it is harder to profile the threads from this service vs. other threads that also use default name

Summary of Changes

Name the threads in this pool, and also add logs to note that the service has stopped/started. These logs will be useful if we ever need to debug the validator process hanging on teardown.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 81.7%. Comparing base (8ad125d) to head (043e1af).

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #35331     +/-   ##
=========================================
- Coverage    81.7%    81.7%   -0.1%     
=========================================
  Files         834      834             
  Lines      224235   224237      +2     
=========================================
- Hits       183390   183344     -46     
- Misses      40845    40893     +48