Create pull-request-bot workflow

[mikealfare]

Problem

We manage a lot of pull requests from internal stories to external bug reports. Some of the associated tasks are deterministic and take time to respond to.

Solution

• create a "pull request bot" that can perform certain actions
• add backport job
• add changelog entry check
• add bot changelog entry job

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

[mikealfare]

won't do