Create new dataset (entity list) or property via the API

[ktuite]

Backend part of these two issues:
getodk/central#575
getodk/central#576

Two new endpoints

POST /v1/projects/1/datasets
{ name: 'trees' }

POST /v1/projects/1/datasets/trees/properties
{ name: 'height' }

Still to do:

• add dataset.create verb and use it
• add documentation

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

Tests.

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

I considered a different endpoint for adding properties. Maybe POSTing an array properties to a dataset, or PATCHing the dataset, but it didn't feel right. One reason is the existing PATCH .../dataset/:name endpoint is used for setting the approvalRequired flag, which feels like it's at a different level than dataset properties. Dataset properties have more to them, and they seem to deserve their own endpoint with POST .../properties.

We could have a matching GET .../properties, but for now, the properties are returned in the main dataset getter.

I tried to gate dataset creation via forms with the dataset.create verb, but it didn't quite make sense. We need to parse the whole form and get the dataset info out, and we would need to pass the auth mechanism along kind of deep inside form.createNew. Also, we have one Dataset.createOrMerge function that handles both new dataset and existing dataset cases, so we don't know if we're creating a dataset or not.

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?

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

Yes, I need to add documentation with this PR. (#1096)

Before submitting this PR, please make sure you have:

• run make test 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]

add dataset.create verb and use it

Once dataset.create is in place, we had talked about the possibility of checking for it in form endpoints in some cases. That feels like a separate issue from getodk/central#575 and getodk/central#576, so I've filed getodk/central#612 about it. I think that change could come in a separate PR.

[matthew-white]

Ah I missed this in the PR description:

I tried to gate dataset creation via forms with the dataset.create verb, but it didn't quite make sense. We need to parse the whole form and get the dataset info out, and we would need to pass the auth mechanism along kind of deep inside form.createNew. Also, we have one Dataset.createOrMerge function that handles both new dataset and existing dataset cases, so we don't know if we're creating a dataset or not.

Could Dataset.createOrMerge() return information about what it did, either creating a dataset or not? If it did, then maybe Forms.createNew() could return that information to the endpoint. That way, the endpoint wouldn't need to pass auth to Forms.createNew(). Just a thought! But I think we could return to these questions later if we decide that we want to make changes as part of getodk/central#612.