Zoekt: Show a warning if there are no nodes connected

Everyone can contribute. Help move this issue forward while earning points, leveling up and collecting rewards.

• Close this issue

Problem to solve

Right now our customers are sometimes confused by the Zoekt Admin UI. It doesn't mention anything about the need to connect Zoekt nodes to start using Zoekt https://docs.gitlab.com/integration/exact_code_search/zoekt/#install-zoekt

Proposal

We should show a warning if we detect that there are no online (connected) Zoekt nodes

cc @IndiraCA