(DOC) add PR template

[bmarwell]

No description provided.

[rmannibucau]

Hi @bmarwell ,

I know it is a common ASF template but I personally hate this verbose checklist increasing a lot the contribution entry cost so I would minimize it as much as possible.
It is also not relevant to run mvn verify for meecrowave.

So I'm tempted, if we want a template, to write a real template and add a link to a doc (website) page for the legal/(i)CLA details.
Maybe something around:

# Issue

<write some description of the issue>

# Solution

<how I solve the issue by this PR>

TIP: if possible link the issue to a jira ticket and ensure the feature/bugfix is tested.

wdyt?