Add iframe security headers

[michaeljguarino]

checking security boxes

Test Plan

regression

Checklist

• If required, I have updated the Plural documentation accordingly.
• I have added tests to cover my changes.
• I have added a meaningful title and summary to convey the impact of this PR to a user.
• I have added relevant labels to this PR to help with categorization for release notes.

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rtc-test-results	Visit	3f86fe1	✅
core-test-results	Visit	3f86fe1	✅
cron-test-results	Visit	3f86fe1	✅
email-test-results	Visit	3f86fe1	✅
worker-test-results	Visit	3f86fe1	✅
graphql-test-results	Visit	3f86fe1	✅

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