Add "getting started/quick start" checklist tour

Created by: erzhtor

Closes https://github.com/sourcegraph/sourcegraph/issues/28322, closes https://github.com/sourcegraph/sourcegraph/issues/32712, closes https://github.com/sourcegraph/sourcegraph/issues/32713, closes https://github.com/sourcegraph/sourcegraph/issues/32714

Description

This PR:

• Migrates existing "getting started tour for visitors" to a new design
• Refactors to support multiple dynamic content
• Adds new "getting started/quick start" checklist tour for authenticated cloud users

Test plan

• SOURCEGRAPHDOTCOM_MODE=true SOURCEGRAPH_API_URL=https://sourcegraph.com sg start web-standalone

1. Check visitors' (non-authenticated) version
   • Open https://sourcegraph.test:3443/search
   • Go through the "quick start" tour
   • Make sure that all steps work as expected, event logs, marked as completed, as well as closing the tour
2. Check authenticated (non-authenticated) version
   • https://sourcegraph.test:3443/sign-in and sign in
   • https://sourcegraph.test:3443/search?feature-flag-key=quick-start-tour-for-authenticated-users&feature-flag-value=true overrides feature flag
   • Go through the "quick start" tour
   • Make sure that all steps work as expected, event logs, marked as completed, as well as closing the tour
   • https://sourcegraph.test:3443/search?feature-flag-key=quick-start-tour-for-authenticated-users removed feature flag override
3. On-prem (not cloud) mode
   • SOURCEGRAPHDOTCOM_MODE=false SOURCEGRAPH_API_URL=https://sourcegraph.com sg start web-standalone
   • Check that no "quick start" tour is shown

NOTE: If you want to reset, delete quick-start-tour local storage variable

Screenshots

Visitors tour	Authenticated tour

App preview:

• Link