Add search to organizations list in admin area

Background

In #419540 (closed) we added an organization overview for instance admins. It does not yet support searching.

Proposal

• Add filtered search bar that only supports text search to start. We can add additional filtering options in future iterations.

• We should also make the OrganizationSelect component in admin/users/components/new_user_organization_field.vue#L50 searchable by removing :searchable="false"

Implementation guide

Needs refinement