Refresh explore space

### Your use case

From testing iA experiments https://github.com/vector-im/element-web/issues/19706 we've learned that people have an appetite for having a richer experience when viewing a space.

**Some key insights**

> "I want to feel I'm part of a community, that the things in this space belong to that space"

> "I can't tell what things I should join...from this curated list of rooms"

**Tasks**

- [ ] For new space members, group suggested rooms and spaces so they can more easily join them in one go to get more out of the space
- [ ] Refocus the page around exploring and discovery of subspaces and rooms to join

**Example mockup**