Add --reseal-on-txs command line option

[kseo]

Specify which transactions should force the node to reseal a block.

• none: never reseal on new transactions
• own: reseal only on a new local transaction
• ext: reseal only on a new external transaction
• all: reseal on all new transactions.

The default is own.

[kseo]

Landed in 0195fe7