Feature: add support for serving from custom path

[Squixx]

Description

I want to run dependency track frontend on a path instead of /, but doing this currently would require to do a full rebuild of the frontend. This PR could be a possible solution direction.

I've seen the reference to:

 // Relative paths cannot be supported. Research by @nscur0 - https://owasp.slack.com/archives/CTC03GX9S/p1608400149085400
  publicPath: '/',

However I can not open this link, so am oblivious to any previous research

I'll update the docs once it's clear this is the way forward

Addressed Issue

https://github.com/DependencyTrack/dependency-track/discussions/1514

Additional Details

setting the BASE_HREF env variable allows you to set a path

Checklist

• [x] I have read and understand the contributing guidelines
• [ ] This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[fnxpt]

similar to #23

[Squixx]

similar to #23

Does that work with oidc? This pr also has working oidc, but I'd be happy if either could move forward

[nscuro]

Sorry for the long wait @Squixx, I'll have a look at this next and have assigned it to v4.12.

[Squixx]

Again sorry for the delay! Overall this looks good to me.

Just a minor nitpick about naming of the env var.

Also, it would be good to add a few words about how to configure this in the docs: https://github.com/DependencyTrack/dependency-track/blob/master/docs/_docs/getting-started/configuration.md#frontend

added docs in https://github.com/DependencyTrack/dependency-track/pull/3899