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.
Also, would it be worth adding the name of the field for other field types - imagine for example you want to include the status, don't you want to display "Status: In Progress" rather than just "In Progress"?

One way to do this would be to have the setting be a dict of dicts:

```
sg_entity_type_extra_display_fields: 
   'Shot': 
      'Sequence': 'sg_sequence.Sequence.code'
      'Status': 'sg_status_list'
      'Sequence Status': 'sg_sequence.Sequence.sg_status_list'
```

With this format you specify the *Label* for each value. In the case above - whenever a shot is displayed, it would print "Sequence:xxx, Status: xxx, Sequence Status: xxx". This syntax is a little bit more involved, but I think it gives a little bit more flexibility for the formatting. What do you think?