Show partitioning warnings more obviously

[danirabbit]

Discussed in https://github.com/elementary/installer/discussions/686

Problem

In the custom partitioning screen, you can see a warning icon on one of the partitions but it wasn't clear to this person how to resolve the warning

Proposal

We should probably should these types of warning messages directly in the view as we've been doing with validated entries instead of using a tooltip or other non-obvious feedback

Prior Art