Fix client missing help messages (backport #4047)

[mergify]

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:

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This is an automatic backport of pull request #4047 done by [Mergify](https://mergify.com).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.06%. Comparing base (8c4f48d) to head (73c5d2a).
Report is 6 commits behind head on maint-0.45.

Additional details and impacted files

@@             Coverage Diff             @@
##           maint-0.45    #4049   +/-   ##
===========================================
  Coverage       74.05%   74.06%           
===========================================
  Files             341      341           
  Lines          106561   106561           
===========================================
+ Hits            78912    78920    +8     
+ Misses          27649    27641    -8     

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