Allow templates to be used for issues opened from alerts

We should allow for templates to be used in conjunction with the automatically opened issues. This would allow for all of the quick actions to be used, which would enable: at mentions, labels, assignees, and more.

This should:

• Provide an extensive amount of customization, leveraging existing features, without making our configuration UI overly complex
• Deprecate the existing mass email based approach, in favor of the at mention model