Relocate feature flags from explore into issue details

[codyde]

Which part? Which one?

Feature Flags

Description

We should move the feature flag section out of Product walkthroughs > Explore and into the Issue > Issue Details section. This will match where FF context will live long term, match the product, and how you'll be able to search FF in the future.

Suggested Solution

Relocate the nav menu item to the issues > Issue details section, specifically for the general docs.

[getsantry]

Auto-routing to @getsentry/product-owners-issues for triage ⏲️

[codyde]

Note - this request came from Sasha / Jasmine.

[codyde]

Note PR submitted - #12453