Transactions generated via dApp wallet connector should have TTL about vm-frontend

[wolf31o2]

From upstream examples:

// set the time to live - the absolute slot value before the tx becomes invalid
txBuilder.set_ttl(410021);

[aryelciu001]

I'll use @wolf31o2 code above for the tx signing

[wolf31o2]

I added an endpoint to get the current absolute slot, too.

[reqlez]

@aryelciu001 is this completed? Can you go thru the issues list and close the ones you know have been completed?

[wolf31o2]

Closed by #345