Add tests

[oliverroick]

NOTE To tests this, you need to run the tests in Node 18

• Adds jest and react-testing-library packages and configuration
• Adds tests for ProfileForm covering serval use cases
• Adds unit tests for form fields

I needed to make a couple of changes to existing code to make the tests work:

• Load xterm and binderhub clients asynchronously
• Change the publicPath so the async modules can be loaded from the correct path

[batpad]

Looks really good to me @oliverroick - thank you.

[batpad]

@yuvipanda this all seems to work really well for me and tests are in place, etc.

I'm going to go ahead and merge this, and then let's discuss next steps / what we'd need to do to get this into production clusters. I know from conversation yesterday you mentioned there's a couple of places already using the Build Your Own Image feature so we might need to make sure all that works as expected - from testing locally, things seem fine, but would likely be good to have a chat / get your eyes on things a bit to see if there's anything more we need to do here before a v1 can roll-out, and I can also do more intensive tests early next week with more "real" environments to ensure everything works.