split up PoS params into sub-keys

[tzemanovic]

Describe your changes

Checklist before merging

• If this PR has some consensus breaking changes, I added the corresponding breaking:: labels
  • This will require 2 reviewers to approve the changes
• If this PR requires changes to the docs or specs, a corresponding PR is opened in the namada-docs repo
  • Relevant PR if applies:
• If this PR affects services such as namada-indexer or namada-masp-indexer, a corresponding PR is opened in that repo
  • Relevant PR if applies:

[codecov]

Codecov Report

Attention: Patch coverage is 98.66370% with 6 lines in your changes missing coverage. Please review.

Project coverage is 73.12%. Comparing base (760462b) to head (c21a67d).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/proof_of_stake/src/storage_key.rs	93.54%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3842      +/-   ##
==========================================
+ Coverage   73.01%   73.12%   +0.10%     
==========================================
  Files         340      340              
  Lines      104750   105192     +442     
==========================================
+ Hits        76488    76917     +429     
- Misses      28262    28275      +13     

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[tzemanovic]

hermes is updated to use this in https://github.com/heliaxdev/hermes/tree/tomas/namada-3842