Added metadata field for video xblocks

[farhaanbukhsh]

This adds an additional field to video xblocks, a field called metadata, where any information related to the component can be used by admin/course-creators.

JIRA tickets: BB-4651

Discussions: Link to any public dicussions about this PR or the design/architecture. Otherwise omit this.

Dependencies: None

Screenshots:

Sandbox URL: TBD - sandbox is being provisioned.

Merge deadline: "None" if there's no rush, "ASAP" if it's critical, or provide a specific date if there is one.

Testing instructions:

1. This pr is based on Koa.3
2. So make sure to have a koa.3 devstack up and running,
3. In the edx-platform repository pull the branch
4. Run make dev.restart-devserver.studio
5. Login to lms at port 18000 and then visit http://localhost:18010
6. Edit the demo course and add another unit, in the new unit add video xblocks
7. Click on Edit on the top and switch to Advance tab
8. Here you can add any data

Author notes and concerns:

None

Reviewers

• @shimulch

[shimulch]

@farhaanbukhsh LGTM 👍

• I tested this: on local devstack I've tested the new metadata field appears, saving to the field persists and import-export works with this field as well.
• I read through the code
• [N/A] I checked for accessibility issues
• Includes documentation
• [N/A] I made sure any change in configuration variables is reflected in the corresponding client's configuration-secure repository.

[farhaanbukhsh]

This is no more needed by NELP so closing this,