Update Pull Request template with breaking change indication

[jpengar]

What type of PR is this?

• subproject management

What this PR does / why we need it:

This PR updates the PR template as done for Commonalities in camaraproject/Commonalities#314

Since some of CAMARA APIs are published as stable implementation of braking changes would require bumping up the main API version.
This should be indicated in the PR. And analyzed in its review.

Which issue(s) this PR fixes:

N/A

Special notes for reviewers:

N/A

Changelog input

 Pull Request template with breaking change indication

Additional documentation

N/A

[AxelNennker]

I think whether a PR introduces a breaking change might be subjective in some cases.
Who decides then whether it is a breaking change?
What are the consequences?

[rartych]

Yes it is often a matter of opinion.
And the PRs often evolve during review.

So I think the first judgement is proposed by author of the PR and then it is verified during the review - codeowners are able to edit the starting comment

[rartych]

It occured in Commonalities that the format of the list with checkboxes is treated by Github as a tasklist.
So PRs are listed with indication of "1 of 2 tasks" completed that can be confusing.

[AxelNennker]

Desided to wait for Commonalities regarding the Action Item issue.