Encode id param on GET

[luisrudge]

Fix #296

Changes

When hitting the management API in endpoints like https://example.auth0.com/api/v2/resource/:id, some of the IDs might need to be encoded, like user ids etc. This PR is a general solution for this issue and it will encode all id params sent to GET requests. To make sure we're backwards compatible and we don't encode something that is already encoded, we're doing a check before encoding the value. This means that:

• if the id param is encoded, we'll do nothing
• if the id param is not encoded, we'll encode it

References

#296

Testing

• This change adds unit test coverage