Disallow creation of frozen clients

[hu55a1n1]

Summary of Bug

We're currently not checking in the create-client handler if the client being created is frozen and I don't think it's in the spec either. Note the spec requires the Tendermint client-state to be initialized with a FrozenHeight: null, but doesn't enforce this in the handler.

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[hu55a1n1]

Related: cosmos/ibc#856

[plafer]

ibc-go doesn't do it either, right?

Then I don't think this is a bug, since our current goal is to be "compliant" to ibc-go 5.0.1.