Adding a person.admin index, and featured_local/community indexes.

[dessalines]

These turned out to make a difference. In my testing, unprimed queries went from ~ 100ms down to 30ms, and primed ones went under 10ms.

Still doesn't address #2994 , but there might not be a good way to do subquery from selects in diesel, and we might have to use the sql_query function for that one.

[phiresky]

Ah I see you added a person.admin index as well. I've added one in #3483 although I also filter the index by where admin to reduce index size.

[phiresky]

@Nutomic ah the create index idx_person_admin on person (admin); index is duplicate now, you should remove one of them (probably the one from this PR because it uses more space)

Edit: i see you commented there