Make the bridge transfer time dynamic based on the chain(s) being used

[parrot9design]

During my testing, the average cross-chain transaction takes anywhere from 20 seconds to 2 minutes.

The Swap and Transfer tabs currently display a transfer time of ~30s for every transaction, which is disingenuous when the rest of the metadata is transaction-specific.

Let's figure out the best way to provide an accurate estimation, whether we run a series of transactions ourselves to get an average for each route (less than optimal), or display the most recent transfer time, like Omm does for the sICX unstaking time:

The main downside of the latter approach is if the last transfer time was quite high, that's what we'll be promoting to users.

[FezBox]

we will revisit this once the new xcall scan API is done