Internal Notes: Technical debt cleanup

During the implementation of Prepare Confidential Notes MVC for GA (&7407), the terminology was changed from confidential notes to internal notes. The code still uses the confidential term in multiple places and this will cause confusion with future maintenance.

On Backend

• Column on the notes table
• API fields (requires deprecation cycle, see #363803 (closed))
• Use in model, services, etc.
• Other...

On Frontend

• Clean up references to internal notes which read as confidential and rename those to internal.

These items can be completed separately. API values should be aliased and the confidential field deprecated by %15.6 in order to be removed in %16.0.