Add Workbench examples on how to use the field

[mikaelpopowicz]

This PR provides some examples on how to use the field :

• as a simple image field
• as an image field in a Nova Repeatable field
• as an image field in a Flexible layout field

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 77.77778% with 4 lines in your changes missing coverage. Please review.

Project coverage is 71.80%. Comparing base (25faafc) to head (8e0276d).

Files	Patch %	Lines
src/FileManager.php	40.00%	3 Missing :warning:
src/helpers.php	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #402 +/- ## ========================================= Coverage 71.80% 71.80% Complexity 274 274 ========================================= Files 44 44 Lines 876 876 ========================================= Hits 629 629 Misses 247 247 ```

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