build: simplify workflows now that all issues are on-call requests

[kdmccormick]

No description provided.

[sarina]

OK since theres no description, this looks like all it does is pull out the "add to board" workflow. I presume because you're updating the board to auto-add all issues from this project?

[kdmccormick]

this PR makes a few changes:

• Like you said, it gets rid of the "add to board" step, as I've updated our GH Project to do that automatically
• It modifies the workflow so that we get tagged and pinged on all incoming. Formerly, it only did that if it looked like a request template was used. This way, we should never miss another incoming request.
• It gets rid of the "Axim Eng Task - internal use only" issue template
• It updates the readme to say that this repo is just for admin requests