Add availability as a separate process

[JonathanGarro]

Currently, the Portal collects a person's availability as part of an existing assignment. Discussions have revealed it would make more sense to keep that as a standalone table in the DB, which people report outside of an assignment.

Let's add a table, linked to an emergency and user, that collect's a person's reported availability and interest. You would navigate to the emergency and click an "I'm Interested in Supporting" button that would then replicate the availability route. The guidance would have to make it clear that when you do that, you're blocking off time to be available for tasks that come in that match your skills.

[JonathanGarro]

I've created a branch for availability that tweaks how people will report when they can support. I created a utility function called get_dates_current_and_next_week that gets all remaining days this week, and all days next week, and asks people when they are available:

[JonathanGarro]

This has been completed. The new feature allows users to:

• Report their availability for the current week (or whatever days remain if accessing it beyond Monday)
• Report next week's availability as it gets closer (currently configured for Thursday)

Also added a trigger to send a Slack message to disaster channels associated with active events requesting members submit their availability with a link included.