Add IBC Ping Pong contract demo

[alpe]

• Adds relay_pingpong_test.go as happy path for Complete IBC Mock testing #255
• Contains contract interface redesign and 🐛 fixes that I had started already

[codecov]

Codecov Report

Merging #259 into alex_ibc_spike2d will increase coverage by 0.35%.
The diff coverage is 31.50%.

@@                 Coverage Diff                  @@
##           alex_ibc_spike2d     #259      +/-   ##
====================================================
+ Coverage             17.08%   17.43%   +0.35%     
====================================================
  Files                    36       36              
  Lines                 11557    11516      -41     
====================================================
+ Hits                   1974     2008      +34     
+ Misses                 9483     9406      -77     
- Partials                100      102       +2     

Impacted Files	Coverage Δ
x/wasm/internal/keeper/ibc.go	9.37% <0.00%> (+0.61%)	⬆️
x/wasm/internal/types/codec.go	44.44% <0.00%> (ø)
x/wasm/internal/types/msg.go	44.69% <0.00%> (+1.31%)	⬆️
x/wasm/internal/types/ibc.pb.go	1.05% <2.77%> (+0.27%)	⬆️
x/wasm/internal/keeper/keeper.go	88.10% <20.00%> (-3.24%)	⬇️
x/wasm/internal/keeper/handler_plugin.go	56.47% <26.74%> (-17.28%)	⬇️
x/wasm/ibc.go	63.15% <97.29%> (+12.13%)	⬆️

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[ethanfrey]

Start review, cover internal package.
Will do follow up review on ping_pong test

[ethanfrey]

Comments on relay test

[ethanfrey]

Let's add a max hits (3 or 4) and if this is higher, then we return IBCPacketReceiveResponse with a "failed" response. In this case, we do not initiate another round. It will allow us to test error handling in acknowledge.

[ethanfrey]

Looks good to merge except for some errand text renamings.

Two things needed in follow-up PRs:

• Run the ping pong until maxValue, so we get an failure and stop. This failure should be properly relayed and not return an error to the ibc handler (and rollback the tx).
• Try version negotiation (ADR25) and see if that works or not - if not, make an issue about it. This can be done separately in a minor PR so we can link the failing code without blocking on it being fixed.

Also submit the issue about ordered channels not working (maybe linking to another intentionally broken pr)