Project Custom Properties tab and ability to create properties

[ktuite]

Closes getodk/central#1870

What has been done to verify that this works as intended?

I've used it along with the backend in getodk/central-backend#1824
I haven't written tests for it yet, though.

Why is this the best possible solution? Were any other approaches considered?

We've discussed a lot of ways to show user properties, and this was the one we decided to start with!

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

This is part of a larger effort to give more flexibility and enable entity segmentation.

Does this change require updates to user documentation? If so, please file an issue here and include the link below.

We will want to add user documentation about what these properties are and how to use them.

Before submitting this PR, please make sure you have:

• run npm run test and npm run lint and confirmed all checks still pass OR confirm CircleCI build passes
• verified that any code or assets from external sources are properly credited in comments or that everything is internally sourced