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

[laurenmrice]

Acceptance criteria

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

• Usage tab
• Code tab

---

Tree view

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

---

Review

• Create PR
• PR reviews