Make all IBC Msg types use pointers

[aaronc]

This is a work-around for missing protobuf definition for some IBC types. At the very least they need to be used in pointer versions (i.e. *MsgCreateClient) to pass protobuf unit tests. Needed for #6213.

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• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes

[codecov]

Codecov Report

Merging #6857 into master will increase coverage by 5.94%.
The diff coverage is 60.95%.

@@            Coverage Diff             @@
##           master    #6857      +/-   ##
==========================================
+ Coverage   55.60%   61.54%   +5.94%     
==========================================
  Files         457      508      +51     
  Lines       27440    31523    +4083     
==========================================
+ Hits        15257    19402    +4145     
+ Misses      11083    10611     -472     
- Partials     1100     1510     +410