[Task] Allow setting a basepath for routes via an environment variable

[aptmac]

It would be nice to allow for a basepath to be set as an environment variable, which would prepend a string to the routes and paths that cryostat-web makes. This would be helpful when nesting cryostat-web inside other applications (the console plugin for example) where there already may be existing pages and routes that would conflict with cryostat-web.

For example, the OpenShift Console has it's own topology view a /topology, so nesting a Topology view from cryostat-web into the Console requires a different route. By setting a basepath of 'cryostat' we can change the cryostat-web route to be /cryostat/topology instead, and avoid route conflicts.

[andrewazores]

Related:

• [Request] Ability to deploy on paths other than the root / cryostat#262
• fix(webpack): set publicPath to / in dev mode #1415
• https://webpack.js.org/guides/public-path/