Adapt logrotate configuration so extra directory is also logrotated

On moma, the current logrotate stanza won't do anything:

root@moma:~# file /var/log/softwareheritage/webapp/swh-web.log
/var/log/softwareheritage/webapp/swh-web.log: ASCII text, with very long lines

And current size is a tad big:

root@moma:~# ls -lah /var/log/softwareheritage/webapp/swh-web.log
-rwxrwx--- 1 swhwebapp swhwebapp 5.7G Oct  5 07:13 /var/log/softwareheritage/webapp/swh-web.log

There is a warning icinga alert about it [1]:

02:01 <+swhbot`> icinga RECOVERY: service disk / on moma.softwareheritage.org is OK: DISK OK - free space: / 4452 MB (23% inode=86%);

• [1] Noticed this week end but it's still a thing

Related to T3313

Test Plan

bin/octocatalog diff (on webapp nodes):

diff origin/production/webapp.internal.staging.swh.network current/webapp.internal.staging.swh.network
*******************************************
+ File[/etc/logrotate.d/swh-webapp] =>
   parameters =>
      "ensure": "file"
      "group": "swhwebapp"
      "mode": "0644"
      "owner": "swhwebapp"
      "content": >>>
# Software Heritage logrotate configuration
# Managed by puppet. Changes will be overwritten.

/var/log/softwareheritage/webapp/swh-web.log {
    weekly
    missingok
    rotate 5
    compress
    notifempty
    su swhwebapp swhwebapp
    postrotate
      kill -USR1 $(cat /var/run/gunicorn/swh-webapp/pidfile)
    endscript
}
<<<
*******************************************
*** End octocatalog-diff on webapp.internal.staging.swh.network

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Migrated from D6407 (view on Phabricator)