Condense Blockstore RPC API datapoints

[steviez]

Problem

Currently, the RPC API that touch the Blockstore emit a datapoint for
each call. For an RPC node serving many requests, these datapoints
could get quite noisy, both in logs as well as traffic to the metrics
agent.

Summary of Changes

So, instead of submitting a datapoint for every call, accumulate the
number of calls in a struct and report that entire struct periodically.

[codecov]

Codecov Report

Merging #34045 (55b823b) into master (47a98eb) will decrease coverage by 0.1%.
The diff coverage is 83.6%.

@@            Coverage Diff            @@
##           master   #34045     +/-   ##
=========================================
- Coverage    81.9%    81.9%   -0.1%     
=========================================
  Files         811      811             
  Lines      219552   219597     +45     
=========================================
+ Hits       179902   179923     +21     
- Misses      39650    39674     +24     

[CriesofCarrots]

Just the one question about counting get_complete_block calls.

[CriesofCarrots]

(sorry, this is the closest place I could add a comment) Should we add a datapoint for get_complete_block()? It would be used when getBlock is called with commitment: confirmed, so potentially quite a lot, although it would also double count on commitment: finalized.
Could be a follow-up, if yes is the answer.

[steviez]

Good point. get_confirmed_signatures_for_address2() could also call get_complete_block() via get_sorted_block_signatures().

I'm tempted to leave things as-is for now as what I introduced is at parity with what we had previously. I think there are several cases of double counts (get_block_time() is called as a subroutine as well), and probably makes sense to review all the methods and come up with a consistent scheme across the board