Systemd needs After as well as Require (#15881)

If the gitea service is stopped because of the db going down
it needs an `After=db.service` to ensure it is restarted in
addition to the `Requires=db.service` to ensure that the db
is started before gitea is started.

Fix #15866

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

contrib/systemd/gitea.service

@@ -7,10 +7,19 @@ After=network.target
 ###
 #
 #Requires=mysql.service
+#After=mysql.service
+#
 #Requires=mariadb.service
+#After=mariadb.service
+#
 #Requires=postgresql.service
+#After=postgresql.service
+#
 #Requires=memcached.service
+#After=memcached.service
+#
 #Requires=redis.service
+#After=redis.service
 #
 ###
 # If using socket activation for main http/s