x/ibc: changelog

[fedekunze]

Description

Add CHANGELOG.md entries for the ibc module and updates to the spec.

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For contributor use:

• 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

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For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #5960 into ibc-alpha will not change coverage by %.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           ibc-alpha    #5960   +/-   ##
==========================================
  Coverage      58.37%   58.37%           
==========================================
  Files            396      396           
  Lines          23510    23510           
==========================================
  Hits           13725    13725           
  Misses          8827     8827           
  Partials         958      958           

[alexanderbez]

ACK

[cwgoes]

ACK