imp: migrate JSON for feemarket

[fedekunze]

Closes: #XXX

Description

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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 #1021 (b8f4000) into main (285c7c4) will increase coverage by 0.00%.
The diff coverage is 63.26%.

@@           Coverage Diff           @@
##             main    #1021   +/-   ##
=======================================
  Coverage   59.15%   59.16%           
=======================================
  Files          79       80    +1     
  Lines        6539     6577   +38     
=======================================
+ Hits         3868     3891   +23     
- Misses       2453     2467   +14     
- Partials      218      219    +1     

Impacted Files	Coverage Δ
client/testnet.go	0.00% <ø> (ø)
x/feemarket/migrations/v010/migrate.go	62.50% <62.50%> (ø)
x/feemarket/keeper/migrations.go	100.00% <100.00%> (ø)