Add "Enqueued" status for NTT transfers

[M-Picco]

NTT transfers might get enqueued when delivered to the destination chain. When the NTT uses Standard Relaying and the message gets delivered we mark it as complete, but the funds might not get unlocked until later, which is a source of confusion for the user. We might benefit from adding a special status "Enqueued" for these transfers.

We'd need logic to query the pertinent contracts on EVMs/Solana to check whether a particular NTT message is enqueued or not. I took some notes on how to do so here, but haven't tried the ideas on code yet.

Also, I think we can narrow it down for VAAs with app ids GENERIC_RELAYER and NATIVE_TOKEN_TRANSFER, since the issue seems to be particular to the relayer scheme