Allow interchain accounts to select a default metadata version

[damiannolan]

Summary

With the introduction of 29-fee, the decision was made to enable relayer incentivization on newly created channels by default. This means that IBC application stacks configured with fee middleware wired in app.go will attempt to enable 29-fee within the ibc handshake protocol unless explicitly directed otherwise by means of the application version field.

Fee middleware is set to enabled upon channel handshakes that include the appropriate 29-fee Metadata struct, JSON encoded into the ibc app version field.

Below is an example 29-fee Metadata JSON for transfer:

{
    "fee_version":"ics29-1",
    "app_version":"ics20-1"
}

Alternatively, an empty string can be provided to create a default 29-fee Metadata and pass an empty string to the base application. IBC applications such as transfer has been adapted to accept an empty string and choose the default version ics20-1, returning it within the OnChanOpenInit callback handler.

Proposal

Currently, passing an empty string for the application version field in 27-interchain-accounts is not supported.

Allow the 27-interchain-accounts controller submodule to select and return a default JSON encoded version metadata by following the method outlined in this draft PR

The controller and host connection IDs can be retrieved internally via the interchain accounts controller keeper using connectionHops[0]. The alleviates the burden of authentication modules being forced to compose their keepers with the IBC core channel keeper.

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