Backend: Users: REST API should report 403 on not found and restricted visibility.

[lnielsen]

Describe the bug

A user that's not found should report 403 instead of 500.

Steps to Reproduce

1. Go to /api/users/10324034
2. See error

Expected behavior

A 403 Error:

{"status": 403, "message": "Permission denied."}

Screenshots (if applicable)

Traceback (most recent call last):
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/flask/app.py", line 2095, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/werkzeug/middleware/proxy_fix.py", line 187, in __call__
    return self.app(environ, start_response)
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/werkzeug/middleware/dispatcher.py", line 78, in __call__
    return app(environ, start_response)
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/flask/app.py", line 2095, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/werkzeug/middleware/proxy_fix.py", line 187, in __call__
    return self.app(environ, start_response)
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/flask/app.py", line 2080, in wsgi_app
    response = self.handle_exception(e)
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/flask/app.py", line 2077, in wsgi_app
    response = self.full_dispatch_request()
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/flask/app.py", line 1525, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/flask/app.py", line 1523, in full_dispatch_request
    rv = self.dispatch_request()
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/flask/app.py", line 1509, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**req.view_args)
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/flask_resources/resources.py", line 65, in view
    return view_meth()
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/flask_resources/content_negotiation.py", line 116, in inner_content_negotiation
    return f(*args, **kwargs)
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/flask_resources/parsers/decorators.py", line 51, in inner
    return f(self, *args, **kwargs)
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/flask_resources/responses.py", line 39, in inner
    res = f(*args, **kwargs)
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/invenio_users_resources/resources/users/resource.py", line 59, in read
    item = self.service.read(
  File "/Users/lnielsen/.virtualenvs/my-site-ZNC6mTtx/lib/python3.8/site-packages/invenio_users_resources/services/users/service.py", line 77, in read
    raise LookupError(f"No user with id '{id_}'.")
LookupError: No user with id '5'.

Additional context