Add optional beta Sliding Sync support

[Just-Insane]

Description

This change introduces a beta implementation of sliding sync support with an toggle to enable it:

config.json

  "slidingSync": {
    "enabled": false
  },

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

[7w1]

Seems like Spaces don't work, as in they simply aren't present for me and all the rooms are thrown into the rooms list. I think that was the only issue I had? Admittedly I was distracted by said issue and tested little else.