User management APIs should use a consistent field name for the partner identifier

[kochhar]

Presently the user and org management APIs use different field names for the same data in different API calls. These should be made uniform.

Eg:

• in createUser the partner identifier is under the field name provider
• in createOrg the partner identifier is under the field name source
• in the JWT auth tokens the partner identifier is under the field name iss

While we cannot change the field name in the JWT token because the spec requires it to be in the iss field, we should adjust the user and org APIs to use a consistent field name.

If provider is not an overloaded term in sunbird, it could be a good standard to adopt for all kinds of partners.