Support configurable attachment size in Application Settings page

What does this MR do?

This MR provides the ability to configure the maximum size of an attachment inside a note. A parameter has been added to the Application Settings page.

Are there points in the code the reviewer needs to double check?

What should be done with the legacy note attachment validation? I added code to make the validation work with the configurable setting. I could see an issue where an admin lowers the limit from 10 megabytes to 5 megabytes, which could cause an existing model to be invalid.

Why was this MR needed?

We often have attachments that exceed 10 MB, and it would be nice to be able to override the defaults.

What are the relevant issue numbers / Feature requests?

See Issue #1258 (closed)

Screenshots

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After: