Add codeowners and basic PR template

[anthony-gomez-fastly]

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

New Feature Submissions:

• Does your submission pass tests?

[anthony-gomez-fastly]

i only added this team, is there a more inclusive one to add or others? @kpfleming

[kpfleming]

For this repo (and also go-fastly and terraform-provider-fastly) the team name should be fastly/devex-engineering.

[anthony-gomez-fastly]

I noticed that there isn't a PR template, i added one that's pretty basic for now, also happy to not include it

[kpfleming]

Looks good to me, with the team name changed.

[philippschulte]

This is great! Maybe it makes sense to add the following sections as well:

• User impact
• Release considerations