Expose last evaluated datetime for flags

### Is your feature request related to a problem? Please describe.

Currently, stale flags are determined based solely on creation date. While it can be helpful, using the date of last evaluation is more correct.

### Describe the solution you'd like.

Store the date of last evaluation for each feature state. Expose it in the UI. Extend workflows stale flags logic to use it, if available.

### Describe alternatives you've considered

N/A

### Additional context

_No response_