feat: v2.0.0 upgrade

[RiccardoM]

Description

Adds the on-chain upgrade handler for the upcoming version 2.0 of Desmos

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Author Checklist

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I have...

• included the correct type prefix in the PR title
• added ! to the type prefix if API or client breaking change
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• provided a link to the relevant issue or specification
• followed the guidelines for building modules
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• included comments for documenting Go code
• updated the relevant documentation or specification
• reviewed "Files changed" and left comments if necessary
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Reviewers Checklist

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I have...

• confirmed the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)

[codecov]

Codecov Report

Merging #629 (a08f49b) into master (1a22342) will decrease coverage by 0.44%.
The diff coverage is 12.19%.

@@            Coverage Diff             @@
##           master     #629      +/-   ##
==========================================
- Coverage   84.23%   83.79%   -0.45%     
==========================================
  Files          91       91              
  Lines        6624     6663      +39     
==========================================
+ Hits         5580     5583       +3     
- Misses        833      866      +33     
- Partials      211      214       +3     

Impacted Files	Coverage Δ
app/app.go	77.70% <12.19%> (-6.90%)	⬇️

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[dadamu]

It is great to me. 👍