Add metrics for rpc send-transaction failures (backport #18156)

[mergify]

This is an automatic backport of pull request #18156 done by Mergify.
Cherry-pick of 64cff8c has failed:

On branch mergify/bp/v1.6/pr-18156
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	both modified:   core/src/rpc.rs

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[mergify]

automerge label removed due to a CI failure

[mergify]

automerge label removed due to a CI failure

[codecov]

Codecov Report

Merging #18163 (bdee779) into v1.6 (57baf7f) will decrease coverage by 0.0%.
The diff coverage is 66.6%.

@@            Coverage Diff            @@
##             v1.6   #18163     +/-   ##
=========================================
- Coverage    82.5%    82.5%   -0.1%     
=========================================
  Files         424      424             
  Lines      117271   117277      +6     
=========================================
- Hits        96827    96799     -28     
- Misses      20444    20478     +34