Add a persistent scope menu for the new left rail menu

Problem to solve

Based on discussion in #382328 (comment 1282284448)

When a navigating to /search, no scope options (i.e. "Projects", "Issues", etc) are presented to the user. This hides information that could be helpful to users in terms of understanding what types of content they can search by. With us moving the search scopes to the left sidebar (#382328 (closed)), this also results in a mostly empty sidebar in this case (which could be better utilized).

Proposal

Show a persistent version of the scopes menu in cases where the a query hasn't yet been entered.

• Base the scope options on the context they are within
  • Any/Any (Global level)
  • Group selected
  • Project selected
• We need to figure out how to show the persistent version of the scopes menu only when the new left rail menu is enabled. (is this needed?)
• We need to figure out how to handle the change of the scope without any search term.