Post additional information to slack for verifying payouts

[fhenneke]

We should make it easier to check the validity of payout transactions.

One easy win is to change

solver-rewards/src/multisend.py

Lines 100 to 103 in 252d732

	print(
	f"Posting transaction with hash"
	f" {safe_tx.safe_tx_hash.hex()} to {safe.address}"
	)

to post to slack instead of just logging the hash.