Add reno for release notes and update CONTRIBUTING guide

[mtreinish]

Summary

Moving forward aqua will be using reno for release documentation. This
commit adds a pro-forma release note and the documentation configuration
to verify release notes moving forward. It also updates the CONTRIBUTING
guide to reflect this new change.

Details and comments

Fixes #990

[Cryoris]

Awesome, thanks! 🎉

[mtreinish]

Once this merges I will add the qiskit-bot configuration to the repo to enable the automation workflow and rename the stable branch stable/0.7 (so the qiskit-bot release automation workflow can do its thing)

[woodsp-ibm]

At some point, hopefully like other common contribution text, this could all go to the common location in docs. Maybe it could already and just state in the elements that this aspect is managed by reno and give a ref.

I think we need a few Labels added for this capability right.

[mtreinish]

My goal is to get everything in docs before too long, after this the only repo left for me to add this to is the ibmq provider then I'll push up the docs change and we can remove it from the local CONTRIBUTING guides for each element. Shouldn't be too long, but until then it'll be good to make sure its documented locally

[mtreinish]

I actually already created the labels for this just now. You can start tagging anything with the Changelog: labels whenever (even after a PR has merged) and when they're included in a release they'll be included in the changelog added to the release page.

[woodsp-ibm]

Thanks Matthew. And I see the Labels now