fix(multisig-protobufs): mark sender field as deprecated and add new field with proper type

[jcs47]

Description

The axelar protobufs for the multisig package have a implementation mistake in which the sender field is declared as a string rather than a byte array. This is not an issue in golang, since in that language the string type is equivalent to the byte array type, and one type can be trivially cast into the other. But this is not the case for all languages, which can create defective code when compiling the protobufs and encoding/decoding the sender field. To solve this problem, this PR replaces the old sender field for a new field with the proper type.

Todos

• Unit tests
• Manual tests
• Documentation
• Connect epics/issues
• Tag type of change
• Upgrade handler

Steps to Test

Expected Behaviour

Other Notes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 39.37%. Comparing base (ee4809d) to head (b49de16).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2232      +/-   ##
==========================================
- Coverage   39.45%   39.37%   -0.09%     
==========================================
  Files         375      375              
  Lines       37417    37417              
==========================================
- Hits        14763    14732      -31     
- Misses      21706    21735      +29     
- Partials      948      950       +2     

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