For #25787 - Display extra info for entities when selecting work area.

Added ability to display extra information for entities in the select work area ui in a similar fashion to the existing functionality for tasks.

For example, you can now specify the following in the environment configuration:

```
sg_entity_type_extra_display_fields: {"Shot":["sg_sequence.Sequence.code"]}
```

which will then result in the Sequence name being shown below the Shot name for each shot when changing work area.  This information is also displayed in the current work area section of the main File manager UI.
what will the output look like for a shot where you grab the additional fields status and sg_sequence.Sequence.code? If I wanted to add sequence to the shots, I think I probably wanted the UI to say "Sequence xxx", rather than "xxx" - perhaps we could add some logic so that if the additional field is a sg link field (dict with name, id and type), it could take advantage of the type info and print out "Sequence xxx" rather than just "xxx" ?