Write Future Work section for 0.15 release notes

[alice-i-cecile]

This should cover at least:

• ghost nodes and UI reactivity
• bevy_cli
• Interaction-yeet
• relations plans
• maybe editor prototypes
• more text plans

I'll tackle the first draft of this, and then others can add it to it.

[Jondolf]

Also constructs, BSN, and other scene improvements

[viridia]

Keyboard focus