Allow suburl to map the application

[HOSTED-POWER]

General information

• OS Platform and Distribution (e.g., Linux Ubuntu 16.04): Debian 10
• ElasticHQ Version: 3.5.12
• Elasticsearch Version: 7.8.0
• Python version (ignore is using docker image):
• Browser Vendor and Version (if applicable):

Issue Description

We would like to map the docker container under a suburl on the host. Eg. https://www.example.com/elastichq

We got this working using reverse proxy , but on the metrics page for example it's not working because it's all mapped under /

Example: https://www.example.com/socket.io/?EIO=3&transport=polling&t=NFa71Al

This above url cannot be found. It's of course because the correct url would be: https://www.example.com/elastichq/socket.io/?EIO=3&transport=polling&t=NFa71Al

It could be solved very easily by allowing a specific mapping url for the container and application. E.g. mappedurl=/elastichq

This could properly set all the paths and it would be an incredible solution to map the monitoring on existing hostnames :)

[HOSTED-POWER]

I assume this would be fixed which would be nice, I'll try to get this tested! :-)