sync gateway: import filter not collections aware

https://docs.couchbase.com/sync-gateway/current/configuration-schema-import-filter.html#upsert-import-filter-function

On this page where it says:

https:://{sgw-uri}/{db}/_config/import_filter

this should be

https://{sgw-uri}/{keyspace}/_config/import_filter

And

put {db}/_config/import_filter

should be keyspace instead of db.
Replacing double colons and this function is keyspace (collection) scoped. This is only
true on Sync Gateway >= 3.1