Deduplicate RPC domain types

[thanethomson]

Closes #918

• 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 #922 (5d3a24c) into master (c8b97aa) will decrease coverage by 0.0%.
The diff coverage is 100.0%.

❗ Current head 5d3a24c differs from pull request most recent head 5783991. Consider uploading reports for the commit 5783991 to get more accurate results

@@           Coverage Diff            @@
##           master    #922     +/-   ##
========================================
- Coverage    70.7%   70.6%   -0.1%     
========================================
  Files         203     203             
  Lines       16230   16241     +11     
========================================
+ Hits        11475   11477      +2     
- Misses       4755    4764      +9     

Impacted Files	Coverage Δ
rpc/src/event.rs	11.4% <ø> (-4.0%)	⬇️
rpc/tests/kvstore_fixtures.rs	95.5% <100.0%> (+<0.1%)	⬆️
tendermint/src/abci/responses.rs	69.5% <100.0%> (ø)
rpc/src/endpoint/blockchain.rs	40.0% <0.0%> (-60.0%)	⬇️
tendermint/src/moniker.rs	70.0% <0.0%> (-30.0%)	⬇️
rpc/src/endpoint/health.rs	20.0% <0.0%> (-30.0%)	⬇️
rpc/src/endpoint/abci_query.rs	17.6% <0.0%> (-3.8%)	⬇️
tendermint/src/config.rs	64.5% <0.0%> (-1.3%)	⬇️
light-client/src/types.rs	30.3% <0.0%> (-0.6%)	⬇️
rpc/src/method.rs	28.8% <0.0%> (-0.5%)	⬇️
... and 5 more

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[xla]

utACK

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