Improve documentation of property sources

[banchan86]

The documentation for property sources could be improved by:

• Providing some application examples/recipes.
• Addressing the common misconception that they automatically update the property in the operator which they originate from.
• Using subjects to avoid branching of property sources for proper initialization of file writers/readers.
• Feeding the original image back into the property source for property editors.

Some old discussions to pull information from:
https://groups.google.com/g/bonsai-users/c/lEj2W_5qgfQ/m/boonkFcyAQAJ
https://groups.google.com/g/bonsai-users/c/Xk7AJajlIyQ/m/yG0CgnfUCAAJ
https://groups.google.com/g/bonsai-users/c/ElLT49caoao/m/yD7aKJaHAgAJ

As they are part of the context menu for the editor, it might be worth including them as part of the Language section of the Bonsai Manual. Could be part of the property mapping article, or maybe a separate article.

[edmundchong]

related to this: to add details about property initialization (which ones are dynamic vs at run-time vs at compile)?
https://github.com/orgs/bonsai-rx/discussions/2346