Fix client missing help messages

[grarco]

Describe your changes

Closes #4022.

Adds a call to arg_required_else_help for TxCustom, TxInitAccount and QueryFindValidator to print the command's help message when no arguments are provided.

Modified QueryFindValidator to carry a single address instead of two and updated the logic of query_find_validator to account for this.

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

All modified and coverable lines are covered by tests ✅

Project coverage is 74.25%. Comparing base (47fc912) to head (f88fb82).
Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4047      +/-   ##
==========================================
- Coverage   74.25%   74.25%   -0.01%     
==========================================
  Files         341      341              
  Lines      107271   107271              
==========================================
- Hits        79651    79650       -1     
- Misses      27620    27621       +1     

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