`GET /{collection}/{obj_uuid}/attributes/{attr}` return type is incorrect

Sorry for spamming this project with issues! However I prefer to document my findings here to keep track of them.

The actual response of the `GET /{collection}/{obj_uuid}/attributes/{attr}` endpoint also returns a `type` property which is not documented here:

https://github.com/HDFGroup/hdf-rest-api/blob/e6f1a685c34ce4db68cdbdbcacacd053176a0136/openapi.yaml#L2221-L2232

Additionally the `openapi.yaml` file defines that the `value` is of type `string`, but in my test setup the server (http://hsdshdflab.hdfgroup.org) returns an `array` of values. This leads to the problem that the returned json string cannot be deserialized properly (there is a type mismatch between `string` and `array`).