Orderby support in entity odata endpoint

[ktuite]

Closes #

Adds $orderby support to OData endpoints for Entities and Submissions. This will be useful overall but it is also part of Frontend showing existing entities in the bulk entity creation flow.

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

Tests

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

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?

New feature for users! We've covered a lot of the OData spec at this point!

Does this change require updates to the API documentation? If so, please update docs/api.md as part of this PR.

Documentation has been updated in this PR.

Before submitting this PR, please make sure you have:

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

[matthew-white]

Is there a way to ensure that the sort is stable? Currently, the ORDER BY clause ends with entities.id DESC, and I think it'd be useful to continue doing that. Though with $orderby, maybe the DESC/ASC after entities.id should match the DESC/ASC that the user specifies for the first $orderby property. 🤔

[matthew-white]

I'm going to add this PR to the project even though getodk/central#589 was the main impetus behind it. It's a nice improvement on its own that we'll want to mention in release notes.

[ktuite]

notes from interactive review with Matt