This PR is a backport of #6418.

For context, `TransactionExtension`, introduced in #3685, is part of the
`stable2412` release, and this PR brings important fixes and quality of
life improvements. Doing the backport now allows us to not break the
interface later.

Opened against #6473 as the changes in the original PR were made on top
of the changes in this backport.

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Signed-off-by: georgepisaltu <george.pisaltu@parity.io>
Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>
Co-authored-by: GitHub Action <action@github.com>