feat: gmp middleware

[adamewozniak]

Description

Add the GMP middleware that allows axelar IBC transactions to submit packets back to axelar.

I know this has no tests - we'll resolve that with: #316

Resolves ojo-network/ojo-evm#6

[codecov-commenter]

Codecov Report

Merging #315 (c116795) into main (5e82697) will decrease coverage by 0.08%.
The diff coverage is 6.71%.

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@@            Coverage Diff             @@
##             main     #315      +/-   ##
==========================================
- Coverage   15.63%   15.55%   -0.08%     
==========================================
  Files          75       78       +3     
  Lines       18454    18655     +201     
==========================================
+ Hits         2885     2902      +17     
- Misses      15435    15616     +181     
- Partials      134      137       +3     

Files	Coverage Δ
x/gmp/keeper/msg_server.go	33.33% <0.00%> (+23.61%)	⬆️
app/gmpmiddleware/types.go	44.73% <44.73%> (ø)
x/gmp/keeper/keeper.go	12.69% <0.00%> (-67.31%)	⬇️
app/gmpmiddleware/handler.go	0.00% <0.00%> (ø)
app/gmpmiddleware/gmp_middleware.go	0.00% <0.00%> (ø)

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