Bug Report or Feature Request (mark with an x)

- [ ] bug report -> please search issues before submitting
- [ x ] feature request

Versions.

Repro steps.

The log given by the failure.

Desired functionality.

Have the possibility to use environment variables in the index.html file

Currently I have google analytics code in the environment files to be able to have different id´s.
This results in some warnings:

"A Parser-blocking, cross site (i.e. different eTLD+1) script, https://www.google-analytics.com/analytics.js, is invoked via document.write. The network request for this script MAY be blocked by the browser in this or a future page load due to poor network connectivity. If blocked in this page load, it will be confirmed in a subsequent console message.See https://www.chromestatus.com/feature/5718547946799104 for more details."

Mention any other details that might be useful.