Make self hosted video poster image and fallback image optional

[abeddow91]

What does this change?

Make self hosted video poster image and fallback image optional

Why?

MAM does not require these fields so this better reflects the state of the atom in CAPI.

This also allows videos in articles to render if a poster image is not available. Previously, videos without a poster image in article returned null to handle the required type.

Screenshots

Before	After

[github-actions]

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[Fweddi]

LGTM - how does this look in a case where a video is trying to fall back to an undefined card picture - a grey box?

[github-actions]

Deploy build 2094 of dotcom:ab-testing to CODE

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• Deploy build 2094 of dotcom:ab-testing to CODE
• Deploy parts of build 2094 to CODE by previewing it first
• What's on CODE right now?

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From guardian/actions-riff-raff.

[github-actions]

Deploy build 28827 of dotcom:rendering-all to CODE

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• Deploy build 28827 of dotcom:rendering-all to CODE
• Deploy parts of build 28827 to CODE by previewing it first
• What's on CODE right now?

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From guardian/actions-riff-raff.

[akash1810]

Please rebase this branch against main before deploying to CODE. #16321 made some changes to CI and infrastructure. Deploying this branch without these changes present will either:

• Fail when using Riff-Raff's default update strategy
• OR delete the new infrastructure if using Riff-Raff's "dangerous" mode

Please rebase this branch against main before deploying to CODE.