Cleaned up and added FM Issue Template and Epic section to the FMM handbook

Why is this change being made?

@lblanchard - Ran this by the FMCs and we think having all our issue templates and epic codes in one place would be helpful. I think it's a bit confusing right now that our only lists live under the micro-campaign process. I have also seen some confusion regarding our old in-person event issue templates, so added a section that indicates which templates are for in-person events only and should not be utilized at this time. If approved, once this section merges, I will remove the current issue template and epic lists under micro-campaigns and link this section under those process details.

Also, I know our new FM epic label will have this showing up in our FM Slack channel once merged, but I think it would be a good idea for a more formal announcement to be made so everyone reviews this page and our new templates. 👀 I'll be updating our micro-campaign/individual tactics and self-service template today as well with the adjustments we made on our virtual templates for consistency.

cc @Helenadixon @lilphil @ttran5

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