Update PULL_REQUEST_TEMPLATE.md to reflect current practices

[pdurbin]

https://github.com/IQSS/dataverse/blob/v4.6.1/PULL_REQUEST_TEMPLATE.md is wildly out of date compared to what we do now. We don't do FRDs any more. We use the magic "connects to" syntax to associate pull requests with issues at https://waffle.io/IQSS/dataverse . In practice, no one is really using the pull request template any more. It's mostly noise.

The main reason I'm opening this issue is that last week I attended a fantastic talk by @christophergandrud about testing called Failing Faster and there was a nice discussion with @mercecrosas and others about how all the automated code coverage stuff I added in #775 might be slightly scary to new contributors because they'll often see a red X on their pull requests like this:

In the example below, the red X is because "Coverage decreased (-0.0002%) to 9.688%"

In PULL_REQUEST_TEMPLATE.md we should probably explain to new contributors that a red X is normal if you haven't written tests and to not worry about it too much. We should, of course, encourage everyone to write tests, which is what #3431 is about.

#2594 is also related but is about updating CONTRIBUTING.md rather than PULL_REQUEST_TEMPLATE.md.

[christophergandrud]

Really nice idea @pdurbin

Actually, we should probably come up with an IQSS "CONTRIBUTING" document that we can include with all of the repos (with project specific modifications) as part of the Software Tools Initiative.

[christophergandrud]

FYI, I've started working on a new repo that will house the overarching IQSS best practices and template documents (e.g. template CONTRIBUTING files): https://github.com/IQSS/social_science_software_toolkit

Please contribute!

[pdurbin]

I just created pull request #3731 and put it in Code Review at https://waffle.io/IQSS/dataverse