config: enable strict cookie secret checking

Signed-off-by: Jakub Sokołowski <jakub@status.im>

templates/grafana.ini.j2

@@ -5,6 +5,8 @@ root_url = https://{{ grafana_domain | mandatory }}/
 
 [security]
 disable_gravatar = true
+cookie_secure = true
+cookie_samesite = strict
 allow_sign_up = false
 admin_user = {{ grafana_username | mandatory }}
 # This works only when container is created the first time