feat: add GB drain upgrade handler

[facundomedica]

Description

closes: #XXXX

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Author Checklist

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• confirmed the correct type prefix in the PR title
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• reviewed tests and test coverage
• manually tested (if applicable)

[codecov]

Codecov Report

Merging #2107 (3757ddd) into main (7f05ad4) will decrease coverage by 0.78%.
The diff coverage is 77.39%.

@@            Coverage Diff             @@
##             main    #2107      +/-   ##
==========================================
- Coverage   75.38%   74.61%   -0.78%     
==========================================
  Files         100      127      +27     
  Lines        8025     9883    +1858     
==========================================
+ Hits         6050     7374    +1324     
- Misses       1589     2007     +418     
- Partials      386      502     +116     

Impacted Files	Coverage Δ
ante/spam_prevention.go	75.92% <ø> (ø)
x/incentive/codec.go	47.82% <ø> (+9.89%)	⬆️
x/incentive/keeper/invariants.go	0.00% <0.00%> (ø)
x/leverage/client/tests/suite.go	100.00% <ø> (ø)
x/leverage/client/tests/tests.go	100.00% <ø> (ø)
x/leverage/keeper/borrows.go	75.93% <ø> (-2.64%)	⬇️
x/leverage/keeper/collateral.go	72.72% <ø> (-0.16%)	⬇️
x/leverage/keeper/errors.go	100.00% <ø> (ø)
x/leverage/keeper/exchange_rate.go	72.72% <ø> (ø)
x/leverage/keeper/genesis.go	87.23% <ø> (ø)
... and 62 more

... and 25 files with indirect coverage changes

[facundomedica]

Ok, now it's better. I just need to run a quick test to double-check that it does what's supposed to 👌

[robert-zaremba]

• upgrade handler should be merged with the "alpha" one.
• I think we can also remove begin/end blocker of GB

[robert-zaremba]

• we should remove begin/end blockers

[robert-zaremba]

approved

[facundomedica]

If we want to remove the begin/end blocker we'll have to do it on the gb module itself. This should be enough imo: umee-network/Gravity-Bridge#10