Finish implementing EntityUpload except for warnings

[matthew-white]

Closes getodk/central#589.

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

This PR includes some changes to tests, but mostly I've just been doing manual testing locally. The QA team will also be taking a look at this PR. I'll be adding more tests as part of #979.

Before submitting this PR, please make sure you have:

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

[matthew-white]

I've pushed a commit that resolves some, but not all of the comments above. Most of the comments that I didn't resolve are a bit fiddly. I don't think they need to be resolved before regression testing begins. I'm going to go ahead and merge this PR, then follow up with another PR later to resolve the remaining comments. These are the comments that are currently remaining:

• [x] https://github.com/getodk/central-frontend/pull/961#discussion_r1562988945
• [ ] https://github.com/getodk/central-frontend/pull/961#discussion_r1568023251
• [ ] https://github.com/getodk/central-frontend/pull/961#discussion_r1568023862
• [ ] https://github.com/getodk/central-frontend/pull/961#discussion_r1572756921