Combine Webhooks and Services settings pages

Resources

PM @victorwu | FE/BE @jivanvl | UX @tauriedavis

Background

Continuation of #25985 (closed) and #23007 (closed).

Scope for this issue

• For a given project, combine the existing Webhooks page and the Services page into a single page.
• Call this single page the Integrations page.
• Update the gear/cog navigation. Combine the Webhooks and Services navigation menu items into one menu item called Integrations.