Improve backport workflow

[offtherailz]

Description

We introduced the backport action. We need to improve the workflow to

• delete the branch after merge has been done
• possibily trigger the checks without needing to close and reopen the PR.
• Auto-link original issue --> this was not possible

Issue already on backport action repo about it to check korthout/backport-action#430

[offtherailz]

For deleting the branches after PR merge, the only solution is this setting in general settings of the repo

Anyway, because will still be able to ber restored, I think it is ok to check it.