Implement Initial JsonApiClient Class

Problem/Motivation

We need to create an initial (and bare bones) ApiClient class that we can extend and build upon. This might end up being taken care of or started by way of https://www.drupal.org/project/api_client/issues/3365959 but this issue can at least be used to validate the requirements for that implementation.

Proposed resolution

* The JsonApiClient class will extend the ApiClient class.
* If an apiPrefix is not provided, 'jsonapi' will be used by default.
* The JsonApiClient class will implement a getCollection method that:
** takes an argument of 'type' (string)
** Makes a request to `${this.baseUrl}/${this.apiPrefix}` to determine the appropriate endpoint for that resource type.
** Fetches data from that endpont, returning data as json.

Remaining tasks

* Implement the ApiClient class
* Define necessary types
* Document the current ApiClient class inline.
* Add test coverage.

API changes

The JsonApiClient class will be created.