backport: rpc-probe updates from #1061

[thanethomson]

Backport of just the RPC probe updates from #1061

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Added entry in .changelog/

[codecov-commenter]

Codecov Report

Merging #1084 (35c25a4) into master (38668f1) will decrease coverage by 0.1%.
The diff coverage is 0.0%.

@@           Coverage Diff            @@
##           master   #1084     +/-   ##
========================================
- Coverage    64.7%   64.5%   -0.2%     
========================================
  Files         238     239      +1     
  Lines       20592   20635     +43     
========================================
- Hits        13332   13330      -2     
- Misses       7260    7305     +45     

Impacted Files	Coverage Δ
tools/rpc-probe/src/common.rs	0.0% <0.0%> (ø)
abci/src/codec.rs	87.8% <0.0%> (-1.4%)	⬇️
testgen/src/header.rs	83.9% <0.0%> (-0.6%)	⬇️
abci/src/server.rs	8.8% <0.0%> (-0.4%)	⬇️
tendermint/src/node.rs	63.7% <0.0%> (ø)
tendermint/src/block/commit_sig.rs	80.3% <0.0%> (+1.9%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 38668f1...35c25a4. Read the comment docs.