PoS: allow to set a receiver target for claim reward tx

[tzemanovic]

Describe your changes

Closes #3965

This transaction can be updated with on-chain governance, but excludes SDK and client changes that require this tx to be deployed first (follow-up in #4427)

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 63.15789% with 14 lines in your changes missing coverage. Please review.

Project coverage is 74.46%. Comparing base (c29fd32) to head (9b01f9a).
Report is 33 commits behind head on main.

Files with missing lines	Patch %	Lines
wasm/tx_claim_rewards/src/lib.rs	0.00%	11 Missing ⚠️
crates/tx_prelude/src/proof_of_stake.rs	0.00%	2 Missing ⚠️
crates/proof_of_stake/src/lib.rs	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4402      +/-   ##
==========================================
- Coverage   74.54%   74.46%   -0.08%     
==========================================
  Files         339      339              
  Lines      110504   110636     +132     
==========================================
+ Hits        82374    82390      +16     
- Misses      28130    28246     +116     

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