feat: add QueryMaxWithdraw and MsgWithdrawMax

[toteki]

This will make withdrawing 100% from frontend easier and less vulnerable to price and uToken exchange rate drift.

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• confirmed the correct type prefix in the PR title
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[codecov-commenter]

Codecov Report

Merging #1642 (01c45c7) into main (7e9ab7a) will increase coverage by 0.12%.
The diff coverage is 54.64%.

@@            Coverage Diff             @@
##             main    #1642      +/-   ##
==========================================
+ Coverage   54.05%   54.17%   +0.12%     
==========================================
  Files          71       71              
  Lines        7150     7483     +333     
==========================================
+ Hits         3865     4054     +189     
- Misses       2988     3115     +127     
- Partials      297      314      +17     

Impacted Files	Coverage Δ
x/leverage/keeper/msg_server.go	10.85% <0.00%> (-1.07%)	⬇️
x/leverage/types/query.pb.gw.go	0.00% <0.00%> (ø)
x/leverage/types/tx.go	0.00% <0.00%> (ø)
x/leverage/keeper/grpc_query.go	62.38% <42.30%> (-0.30%)	⬇️
x/leverage/keeper/keeper.go	66.41% <50.00%> (ø)
x/leverage/keeper/limits.go	41.11% <54.23%> (+25.48%)	⬆️
x/leverage/keeper/oracle.go	64.13% <71.42%> (+1.05%)	⬆️
x/leverage/keeper/liquidate.go	83.62% <84.61%> (+0.59%)	⬆️
x/leverage/client/tests/tests.go	100.00% <100.00%> (ø)
... and 3 more

[robert-zaremba]

Only reviewed the proto

[toteki]

Added some comments to guide reviewers. Let's get this merged quickly

[robert-zaremba]

utACK