[7434] - FE/BE Structured data field for Mozfest pages

[stevedya]

Closes #7535, #7536 , #7434

Implementation Checklist:

• Text field in Promote tab where JSON can be added
• Add link to Structured Data tester in help text
• Print out schema into a block in the template
• Ensure structured data is stripped of all tags

Of Note:

• Commented out a line in an old migration because it was causing issues with the CI. Please see this comment for details.

Changes in Models:

• Did I squash my migration?

Screenshots:

Putting valid Structured Data JSON will be properly detected by tools used to check Structured Data.

Putting potentially malicious <script> tags (or invalid JSON) will just cause the Structured Data to be invalid but will not affect the user.

[github-actions]

This PR introduces visual differences. Click here to inspect the diffs.

[b-ggs]

Mistakenly closed, apologies.

[b-ggs]

Mistakenly closed, apologies.

[github-actions]

This PR introduces visual differences. Click here to inspect the diffs.

[Pomax]

I notice this is still a draft with CI failing, I'll unmark myself for review for now, please reflag me when this PR is ready for review?

[stevedya]

Hey @Pomax you can take a look now whenever you get the chance 🙂 I may need @b-ggs's assistance with these CI fails as well.

[github-actions]

This PR introduces visual differences. Click here to inspect the diffs.

[github-actions]

This PR introduces visual differences. Click here to inspect the diffs.

[b-ggs]

Unassigning Pomax from this for now. Need to look into why the Wagtail CI along with the others are failing.

[richbrennan]

@Pomax

I don't think Sabrina's review is required now that Marc has approved it, can this be merged (code freeze depending)?

[sabrinang]

+1 you can remove me as reviewer since Marc has reviewed/approved.

[Pomax]

approved, but holding off landing until we're out of code freeze

[Pomax]

migration numbering updatred, and reapproved for post-code-unfreeze merge

landing.