feat: backend approach for access control options

[mariajgrimaldi]

Description

This PR adds new fields to the sequence metadata so a client can use it to control a student's access:

  "metadata":
       {
           …
           "is_access_controlled": true,
           "access_control_type": "password",
           "access_control_allowed_values": "1234,1235"
       },

Which view to be rendered would depend on access_control_type, which can be password, IP range, or Secure Web Browser.

Here's an outline of the technical proposal: https://docs.google.com/document/d/16qIS1LDl-STp0WJZk4swUb2y7ShFZE0Lec7iZiTwVFo

Supporting information

More context on the product proposal can be found here: https://openedx.atlassian.net/wiki/spaces/COMM/pages/3928293395/New+ways+of+restricting+access+to+subsections

Testing instructions

1. Move to this branch
2. Run: tutor dev exec lms shell && ./manage lms migrate learning_sequences
3. Make a POST call to save your sequence metadata with the new fields we just added:
   POST <STUDIO_URL>/xblock/<USAGE_KEY>
   Here's an example:
   
4. You can get the sequence metadata by calling:
   GET <STUDIO_URL>/xblock/<USAGE_KEY> with the header Accept: application/json