Add some comments in the backporting pull request

[lampajr]

Allow users to add extra information in the generated backporting pull request as comments.

[tarilabs]

for instance here:

I did not realize what to do, beyond reviewing the code as requested by the bot.

Then Tristan here shown me it was enough to trigger the CI manually: https://github.com/kiegroup/drools/pull/5408#issuecomment-1653022109

So in addition to

Backport: #5406

it would be helpful to add some further instructions such as "please manually approve/run the CI with the usual comments"

[lampajr]

@tarilabs thanks a lot for the example, in the specific case you mentioned - as user - would you prefer to have the further instructions as new separated comment in the pr or as part of the pr description?

[tarilabs]

_ as part of the pr description_ would work perfectly for me, please

[tarilabs]

ie: just before/after the "Backport: #5406" and not in the <details/>