feat(curated recommendations): [MC-1520] Add `isTimeSensitive` to corpus GraphQL query

[nina-py]

References

JIRA: https://mozilla-hub.atlassian.net/browse/MC-1520

Description

Make incremental progress on the "Need to Know" prototype by adding the field we will be differentiating the data by, isTimeSensitive, to the GraphQL query that fetches curated recommendations.

• Added new field to the Curated Corpus Graphql query

• Updated CorpusItem and CorpusRecommendation classes

• Updated existing tests and sample test data

PR Review Checklist

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• [x] This PR conforms to the Contribution Guidelines
• [x] The PR title starts with the JIRA issue reference, format [DISCO-####], and has the same title (if applicable)
• [ ] [load test: (abort|warn)] keywords are applied (if applicable)
• [ ] Documentation has been updated (if applicable)
• [x] Functional and performance test coverage has been expanded and maintained (if applicable)