agreement: add counters for dropped tasks and slow responses

[cce]

Summary

In #2741 we added some additional logging for cases where the pseudonode tasks queues (used by MakeVotes and MakeProposals) were full, or if the cryptoVerifier response queue was full, or if it was taking more than 2s to wait for a verifier task to return. This adds counters to accompany those log messages.

Test Plan

Existing tests should pass.

[codecov-commenter]

Codecov Report

Merging #3861 (9977349) into master (0146fff) will increase coverage by 0.01%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master    #3861      +/-   ##
==========================================
+ Coverage   49.95%   49.97%   +0.01%     
==========================================
  Files         393      393              
  Lines       68353    68359       +6     
==========================================
+ Hits        34149    34160      +11     
+ Misses      30473    30469       -4     
+ Partials     3731     3730       -1     

Impacted Files	Coverage Δ
agreement/cryptoVerifier.go	69.71% <0.00%> (+1.63%)	⬆️
agreement/pseudonode.go	70.07% <40.00%> (-0.56%)	⬇️
catchup/service.go	69.38% <0.00%> (+0.49%)	⬆️
cmd/tealdbg/debugger.go	72.41% <0.00%> (+0.98%)	⬆️
agreement/proposalManager.go	98.03% <0.00%> (+1.96%)	⬆️

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