Add rich member details to organization data sources

Currently, an organization data source just contains the members of the organization as a set of their IDs. On the other hand, group data sources currently contain a set of rich user objects, containing more information about the user such as email and username. Unfortunately, the information for each user retrieved by the Group API differs from the Organization API.

Going forward, we should decide on a single set of fields that members retrieved via organizations and groups will contain. This may require changes to the Organization API, or an additional request for each member of the org. For example, email is not included in an `codersdk.OrganizationMemberWithName` instance.