Getting started tour improvements

Created by: erzhtor

Closes https://github.com/sourcegraph/sourcegraph/issues/29890.

Description

This PR:

• Adds new disable-search-onboarding-tour feature flag for disabling old search onboarding tour
  • Ex: /search?feature-flag-key=disable-search-onboarding-tour&feature-flag-value=true will disable locally
• Adds multiple feature flags override support through URL search parameters
  • Ex: /search?feature-flag-key=my-feature1,my-feature-2&feature-flag-value=false,true
• Getting started onboarding tour
  • Adds languages support + refactors to use zustand as a store
  • Adds support to show additional info dialog in search results
  • Minor content re-ordering/changes

How to test

• sg start web-standalone
• https://sourcegraph.test:3443/search?feature-flag-key=disable-search-onboarding-tour,getting-started-tour&feature-flag-value=true,true
• Check that the old onboarding tour is not shown anymore (try in incognito mode, since there are other conditions to show or not for this onboarding tour)
• Check that getting started onboarding tour works with new languages support

Note: for now only "Search diffs for added code" has lang-specific links, rest of items to be updated, waiting for the content.