Add -l/--label-change option to sendpayment.py to automatically label change address

[kristapsk]

Also added typehints to direct_send().

[kristapsk]

If nobody wants to review / test this, I plan to merge this soon, should not affect any existing functionality.

[AdamISZ]

Looking now.

[AdamISZ]

I agree with the rest apart from the above two comments.

However, as with all such UI type changes, it makes sense to include an adaptation to both Qt and, especially, to the RPC interface, to allow clients to use them.

[kristapsk]

as with all such UI type changes, it makes sense to include an adaptation to both Qt and, especially, to the RPC interface

Agree, but that can be done in a follow-up PRs, created separate issues for RPC API and Qt GUI.

[AdamISZ]

Will test 34c0c45

[AdamISZ]

I have tested both --label-change="XXX" and -l YYY options to sendpayment.py using both direct send -N 0 and normal coinjoin defaults, on both signet and mainnet.

tACK 34c0c45