Add an empty state when searching projects returns no results

[gtsiolis]

Problem to solve

Following up from #5318 (comment), when project search returns no results the new project card is visible. When project search returns no results there's no proper user feedback about this or no action suggested.

Proposal

Instead, we could a) hide the new project card and b) add a minimal empty state like the one in #5022 with a link to create a new project.

[stale]

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[gtsiolis]

This seems to be half-resolved now. However, we still need a basic empty list placeholder when there are not results.

Re-posting the proposal:

Instead, we could a) hide the new project card and b) add a minimal empty state like the one in #5022 with a link to create a new project.

Also, updated the issue title to be more specific about the other half of this proposal.

Cc @jldec based on our last discussion on search, see relevant notes (internal)