use AnyClientState enum instead of allowing only TmClientState

[rnbguy]

Just like AnyConsensusState, we should use AnyClientState.

This was not possible before because the ClientState derive macro didn't take relevant type bounds for IbcContext<S>. When the next ibc version is released, we can derive ClientState on AnyClientState enum as follows:

#[derive(ClientState)]
#[validation(IbcContext<S: Store + Debug>)]
#[execution(IbcContext<S: Store + Debug>)]
pub enum AnyClientState {
    Tendermint(TmClientState),
    SoloMachine(SmClientState),
}