chore: update project's PR template

**Is your feature request related to a problem? Please describe.**
As we will be cleaning up substantially the CI and improve the developer experience, update the pull request template.

**Describe the solution you'd like**
TBD
**Describe alternatives you've considered**
Leave it as is, possibly outdated

part of cleanup https://github.com/hyperledger-cacti/cacti/issues/4037