[Feature Flags] Notification: add feature flag content to Usage and Code tabs

[laurenmrice]

Acceptance criteria

Note: Before creating a PR for this issue, ensure that there are no current PRs in review that could conflict with these pages.

Create a PR to add feature flag content sections to Notification on the following tabs:

• Usage tab
• Code tab

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Notification

Usage tab

• Add a "Feature flag" tag to the top of the page, right above the "Description".
  *This may require dev help. Refer to the Figma spec.

### Feature flags

• Add net new section
• Add section heading
• Add content from Figma file

Code tab

• Add a "Feature flag" tag to the React resource card.
  *This may require dev help. Refer to the Figma spec.

### Feature flags

• Add net new section
• Add section heading
• Add content from Figma file

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Review

• Create PR
• PR reviews

[Kritvi-bhatia17]

This issue is on hold until Benjamin's Notifications PRs (#4218, #4243 and #4270 ) are merged.