Simplify UToronto hub deployment so it is easier to manage

[yuvipanda]

UToronto was one of our very first hub deployments, and we have experimented with a bunch of different things since that make adminstering to hubs much simpler. A lot of progress has already been made on this front (#638), but a couple more will make our life even easier!

Remove Dockerfile from UToronto image

The utoronto-image uses a custom Dockerfile to build. This was mostly because of missing bits of R support in repo2docker when the image was first constructed - primarily, newer R versions and binary package installs. I've since worked on bringing repo2docker's R support up to par, and we can switch to using it now! This will simplify maintenance of the image

Switch to using CILogon for auth instead of AzureAD

This would need to be CILogon directly rather than via Auth0, and we should restrict the supported Auth providers to just UToronto + something that 2i2c engineers can use to log on. This makes testing and other adminstration easier for 2i2c engineers, and removes the need to renew the AzureAD credentials once every year. We will need to find a way to match the current user account names (they use oids from AzureAD, not emails) - if we can't, this is a non-starter

[choldgraf]

When the PR below is merged, we should be able to start prototyping using CILogon for U.Toronto authentication:

• Full Cilogon integration #1089

[damianavila]

From a support ticket where a conversation about the timeline for big changes happened:

Re: timing, given it's a drastic change, how do you feel about aiming for the next break in classes? Looking at https://artsci.calendar.utoronto.ca/sessional-dates, perhaps first week of January is a good time to deploy those? If that sounds good, we can start planning for that.

And it seems they confirmed it is a good time for them, although I would argue it could be a hard time for us from a capacity point of view.

[yuvipanda]

Yeah, I agree - unfortunately that is often the only time to be able to do this (from personal experience at berkeley too). The goal is to spend the next 3 months staging and planning these, so first week of january is just rollout.

[damianavila]

Shapping this one is necessary, assigned to @yuvipanda.

[damianavila]

We can close it by now thanks to all the work @yuvipanda has concreted around this one.