Add instrumentation details to General -> Settings -> Analytics settings

Proposal

In Determine where to put the instrumentation deta... (#390109 - closed) we determined the MVC for adding Instrumentation Details would be to add it alongside the existing Product Analytics settings in Settings -> General. This is the implementation issue to add that interface and navigation as shown in the design.

Design

See #390109[general-settings-product-analytics.png]

Implementation plan

Wait for Add Project-level settings (!117701 - merged) to be merged, this adds new "Product analytics" section to Project -> Settings -> General.

• Extract instrumentation instructions to new standalone component
• Add instrumentation settings section inside product analytics settings section ee/app/views/product_analytics/_project_settings.html.haml
  • if no instrumentation key exists, show "Set up" button which links to onboarding flow
  • else embed the instrumentation_instructions.vue for configuring instrumentation details
  • tests
  • documentation

Update settings to match latest designs

Implement separately: #407126 (closed) Implemented together as the first change didn't look great on its own

• update copy, combine code snippets, remove collapsible sections