Option to enable URL previews by default in E2EE rooms

**Is your feature request related to a problem? Please describe.**
It is frustrating/confusing that Element includes a setting "Enable inline URL previews by default", but this actually only applies to rooms that are not E2EE. URL previews in E2EE must be individually enabled in every room.

**Describe the solution you'd like**
1. Make it clear that the setting above only applies to non-E2EE rooms.
2. Add another option to "Enable inline URL previews by default in E2EE rooms"

**Describe alternatives you've considered**
Apply the above option to E2EE by default. This would potentially impact privacy expectations.

Making it easier to see an individual previews (or to enable URL previews in E2EE rooms) by a call-to-action on a link without a URL preview could also help ease this problem.

**Additional context**
https://matrix.to/#/!ZCWYLfAKXolsPWObuZ:matrix.org/$4MFfmETy2oUY5RcT1DLpUDmg5gWAd8zRze9qsyhoynQ?via=matrix.org&via=element.io&via=vector.modular.im

No implementation files or tests are identified in the issue. Start by locating the existing "Enable inline URL previews by default" setting and the per-room E2EE URL-preview control in the relevant Element client, then check how privacy expectations are documented. Done means the non-E2EE scope is clear and E2EE rooms have a separate default option without changing their privacy behavior implicitly.

Written by the indexing model from the issue text.