Talk Web upgrade for Talk Desktop compability

[ShGKme]

Add a minimal amount of changes in Talk Web to make it compatible with the Talk Desktop build.

• https://github.com/nextcloud/spreed/pull/9050
  • [x] Add IS_TALK_DESKTOP constant
  • [x] Add Electron to supported browsers / Disable browser check on Desktop
  • [x] Separate Webpack config to common and web
• https://github.com/nextcloud/spreed/pull/9051
  • [x] Fix absolute links for conversations
• https://github.com/nextcloud/spreed/pull/9054
  • [x] Fix the current conversation removing redirect
• DRAFTS
  • [x] Do not reload a page on the session error handling
  • [x] Do not reload a page on the signaling error handling
• [x] Temporary disable unsupported features
  • [x] Disable avatar contacts menu until #34 is resolved
  • [x] Disable screensharing until #11 is resolved
• [ ] https://github.com/nextcloud/spreed/issues/8715