Add registered_at timestamp

[dunkOnIT]

Notes:

Everything here seems to work, the main question I have is when to populate registered_at - I see two options:

1. Time at which the reg request was submitted?

• Just because someone submits a request doesn't mean they've registered

2. Current time at the point of creating the registration?

• This is what I intuitively want to use, but then: Why are we not using created_at with an increased precision value?

Until we have an answer to this, I'm using a very direct approach - getting the db to populate registered_at when the row is created. I don't love this approach, because it isn't exposed in the code/editable later - but something like an after_create hook feels very redundant (given that we have created_at) with my current understanding, so I just went with something simple while we discuss the implementation.

TODO

• Add & populate migration
• Populate registered_at when reg is created
• Display registered_at in the frontend