jsonrpc/usersvc: use best block height/time in view call

[jchappelow]

Alternative to #1088
Resolves #1084

action get_post($id) public view {
    SELECT *, @block_timestamp as stamp, @height as height
    FROM posts
    WHERE id = $id;
}

 $  kwil-cli database call -i xc4503ccf15daada96e36cbbacf641f48ebc6226e28906c8757866b91 -a get_post 'id:3'
| content | height | id |   stamp    | title  | user_id |
+---------+--------+----+------------+--------+---------+
| hihi    |    842 |  3 | 1732569623 | title2 |       1 |

$  kwil-cli database call -i xc4503ccf15daada96e36cbbacf641f48ebc6226e28906c8757866b91 -a get_post 'id:3'
| content | height | id |   stamp    | title  | user_id |
+---------+--------+----+------------+--------+---------+
| hihi    |    843 |  3 | 1732569630 | title2 |       1 |

[brennanjl]

@jchappelow could you also backport to preview?

[jchappelow]

Sure, just a sec.