database: always include table name in SELECT

When JOINs are performed on the auto-generated SELECT query,
multiple tables may have the same field names. For instance, in
lists.sr.ht the "list" and "subscription" tables both have an "id"
column. When performing a "mailingLists" GraphQL query this results
in this error:

    pq: column reference "id" is ambiguous

The old query looks like this:

    SELECT "description", "name", "id", "owner_id", "updated", COALESCE(
    access.permissions,
    CASE WHEN list.owner_id = $1
    THEN $2
    ELSE CASE WHEN sub.id IS NOT NULL
    	THEN list.subscriber_permissions
    	ELSE null END
    END,
    list.nonsubscriber_permissions | list.account_permissions), access.id AS access_id, sub.id AS subscription_id FROM list LEFT JOIN access ON
    access.list_id = list.id AND
    access.user_id = $3 LEFT JOIN subscription sub ON
    sub.list_id = list.id AND
    sub.user_id = $4 WHERE list.owner_id = $5 ORDER BY "updated" DESC LIMIT 26

The new query looks like this:

    SELECT "description", "name", "list"."id", "list"."owner_id", "list"."updated", COALESCE(
    access.permissions,
    CASE WHEN list.owner_id = $1
    THEN $2
    ELSE CASE WHEN sub.id IS NOT NULL
    	THEN list.subscriber_permissions
    	ELSE null END
    END,
    list.nonsubscriber_permissions | list.account_permissions), access.id AS access_id, sub.id AS subscription_id FROM list LEFT JOIN access ON
    access.list_id = list.id AND
    access.user_id = $3 LEFT JOIN subscription sub ON
    sub.list_id = list.id AND
    sub.user_id = $4 WHERE list.owner_id = $5 ORDER BY "updated" DESC LIMIT 26

database: expand field map for composite fields

This allows models to fetch multiple SQL columns to obtain the data
necessary to compute a single composite GraphQL field, while still
avoiding unnecessary fetches if those fields are not queried.

Import GQL server interfaces from gql.sr.ht