Feature: Add support for a different base URL

[pratikborsadiya]

Use Case

I want to deploy UI behind a proxy on a sub URL. Like https://www.myurl.com/hypertrace

Problem

When the UI is deployed behind a sub URL all CSS and JS assets fail to load with 404 error as the base URL is specified as / in index.html

Proposal

Having an environment variable for base URL would solve the issue

[aaron-steinfeld]

This could go in the helm config or both the helm config and dockerfile if using the image directly. Would accept PRs for either.