The pagination on the user dashboard sounds unnecessary, this will
change it to a prev/next buttons. For instances with around `10 million`
records in the action table, this option affects how the user dashboard
is loaded on first visit.
---------
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>
Two SQLs are very slow when `action` table have over 5M records.
```
database duration=1.8881s db.sql="SELECT created_unix DIV 900 * 900 AS timestamp, count(user_id) as contributions FROM `action` WHERE user_id=? AND act_user_id=? AND (created_unix > ?) GROUP BY timestamp ORDER BY timestamp"
database duration=1.5408s db.sql="SELECT count(*) FROM `action` WHERE (user_id = ?) AND (is_deleted = ?)"
```
This will cache the count for the first loading or when the activities
changed.
