Filter issue boards by name in the dropdown
Description
Possible improvement of https://gitlab.com/gitlab-org/gitlab-ee/issues/4916.
Having issue boards sorted by name is already really helpful, but we can do even more by allowing filtering for patterns, as we already have when selecting labels. This will speed up the search in case of very huge lists.
Proposal
Implement search feature in the issue board list dropdown, similar to what we already have for labels.