Decide on validation for merkle path prefix in MsgProvideCounterParty

[DimitrisJim]

Raised by Aditya in #6982 (comment)

We should probably validate the merkle path prefix as well. Unclear what exactly we should check yet. Let's make an issue for it so we don't lose track of it.

Will be handled by ibc-go team.

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[DimitrisJim]

Note that current validation in Counterparty simply asserts that MerklePath is not empty, this is what the validation for connections did previously.

Slapping needs-discussion label on this and if we decide the current check suffices, we can close the issue.

[colin-axner]

Well, correct me if I am wrong, but all path elements must be non-empty except the last?

In addition, we could do length restriction on each path element, but it would be arbitrary

[crodriguezvega]

Closed by #7193