Add support for secp256k1 consensus keys

[mkaczanowski]

Closes: #1364

This adds the support for parsing secp256k1 consensus key from priv_validator_key.json.

A while ago I've merged support for secp256k1 consensus key type to tmkms mainly for band protocol network. It came out that the functionality to import the private key from tendermint format to tmkms doesn't work due to lack of support in tendermint-rs.

• [x] Referenced an issue explaining the need for the change
• https://github.com/iqlusioninc/tmkms/issues/761
• [x] Updated all relevant documentation in docs
• to the best of my knowledge
• [x] Updated all code comments where relevant
• [x] Wrote tests
• [x] Added entry in .changelog/

[codecov-commenter]

Codecov Report

Merging #1358 (f9b0a55) into main (4d81b67) will increase coverage by 0.5%. Report is 1 commits behind head on main. The diff coverage is 44.7%.

:exclamation: Current head f9b0a55 differs from pull request most recent head 7ff521d. Consider uploading reports for the commit 7ff521d to get more accurate results

@@           Coverage Diff           @@
##            main   #1358     +/-   ##
=======================================
+ Coverage   59.8%   60.4%   +0.5%     
=======================================
  Files        274     275      +1     
  Lines      27254   27062    -192     
=======================================
+ Hits       16314   16361     +47     
+ Misses     10940   10701    -239     

Files Changed	Coverage Δ
tendermint/src/abci/response/process_proposal.rs	0.0% <0.0%> (ø)
...dermint/src/abci/response/verify_vote_extension.rs	0.0% <0.0%> (ø)
tendermint/src/abci/types.rs	0.2% <0.0%> (-0.1%)	:arrow_down:
tools/proto-compiler/src/constants.rs	0.0% <ø> (ø)
tendermint/src/private_key.rs	45.0% <50.0%> (+19.0%)	:arrow_up:
config/tests/mod.rs	100.0% <100.0%> (ø)
tendermint/src/public_key.rs	79.5% <100.0%> (+3.1%)	:arrow_up:

... and 6 files with indirect coverage changes

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