Unification and allowedHosts in local dev

[RaananW]

I got a request to add allowedHosts to our dev server as an extra measure of security.

This PR unifies dev-server generation in all of our webpack configurations, and, of course, add allowedHosts as an optional environment variable.

After this is merged you will need to run npm install to get everything to work correctly.

[RaananW]

CC @RolandCsibrei

[bjsplat]

Please make sure to label your PR with "bug", "new feature" or "breaking change" label(s).
To prevent this PR from going to the changelog marked it with the "skip changelog" label.

[bjsplat]

Snapshot stored with reference name:
refs/pull/14440/merge

Test environment:
https://babylonsnapshots.z22.web.core.windows.net/refs/pull/14440/merge/index.html

To test a playground add it to the URL, for example:

https://babylonsnapshots.z22.web.core.windows.net/refs/pull/14440/merge/index.html#WGZLGJ#4600

Links to test babylon tools with this snapshot:

https://playground.babylonjs.com/?snapshot=refs/pull/14440/merge
https://sandbox.babylonjs.com/?snapshot=refs/pull/14440/merge
https://gui.babylonjs.com/?snapshot=refs/pull/14440/merge
https://nme.babylonjs.com/?snapshot=refs/pull/14440/merge

To test the snapshot in the playground with a playground ID add it after the snapshot query string:

https://playground.babylonjs.com/?snapshot=refs/pull/14440/merge#BCU1XR#0