More fixes for relative urls when running Grafana under a different sub path (#10470)

* Add nginx proxy docker container

Ease test/verification of running Grafana thru a reverse proxy

* Add apache proxy docker container

Ease test/verification of running Grafana thru a reverse proxy

* Fix relative urls for reset password page

* Fix relative urls for signup page

* Fix relative urls for login page

* Fix relative urls edit plugin page

docker/blocks/apache_proxy/Dockerfile

@@ -0,0 +1,4 @@
+FROM jmferrer/apache2-reverse-proxy:latest
+
+COPY ports.conf /etc/apache2/sites-enabled
+COPY proxy.conf /etc/apache2/sites-enabled