Simplify quickstart page and related documentation

[mintlify-development]

Original Instruction: simplify the quickstart page

This PR simplifies and streamlines our documentation, focusing on the quickstart page and related content. Changes include:

• Simplified quickstart.mdx for better user onboarding
• Updated related documentation files for consistency
• Streamlined content across multiple sections including:
  • User authentication docs
  • API Playground
  • Content components
  • Analytics integrations
  • SDK integrations
  • Development and migration guides

Modified files:

• Quickstart and core docs:

  • quickstart.mdx
  • development.mdx
  • migration.mdx
  • reusable-snippets.mdx

• User Authentication:

  • advanced/user-auth/oauth.mdx
  • advanced/user-auth/shared-session.mdx

• API Playground:

  • api-playground/mdx/configuration.mdx
  • api-playground/openapi/setup.mdx
  • api-playground/openapi/writing-openapi.mdx

• Components:

  • content/components/accordions.mdx
  • content/components/mermaid-diagrams.mdx
  • advanced/widget/chat.mdx

• Integrations:

  • Analytics:
    • integrations/analytics/overview.mdx
    • integrations/analytics/google-analytics.mdx
    • integrations/analytics/google-tag-manager.mdx
    • integrations/analytics/posthog.mdx
  • Privacy:
    • integrations/privacy/osano.mdx
  • SDKs:
    • integrations/sdks/speakeasy.mdx
    • integrations/sdks/stainless.mdx