Add FEATURE_FLAG_REPORT_ISSUE_ENABLED to gate Report Issue menu item

[fmontes]

Description

Add a feature flag to control visibility of the "Report an Issue" entry added to the user toolbar menu in PR #35717. The flag should hide the menu option when set to false.

Acceptance Criteria

• New feature flag key FEATURE_FLAG_REPORT_ISSUE_ENABLED is defined in FeatureFlagName.java and whitelisted in ConfigurationResource
• Frontend FeaturedFlags enum exposes the new key
• When the flag is false (default), the "Report an Issue" item is not rendered in the toolbar user menu
• When the flag is true, the menu item appears and opens the report issue dialog as before
• Unit tests cover both enabled and disabled states
• Flag check is implemented in the component (not the store) so it can be cleanly removed after launch

Additional Context

Follow-up to #35717. Flag defaults to off (opt-in) — must be explicitly enabled in dotmarketing-config.properties to show the menu entry.

[github-actions]

PRs linked to this issue

• feat(report-issue): gate toolbar menu item behind FEATURE_FLAG_REPORT_ISSUE_ENABLED by @fmontes