Improve the 404 friendly message

[HowardWolosky]

Description

Doing some clarifying wording in the friendly error message that we add to a 404 to indicate that they could be getting the error because the item truly doesn't exist, not simply due to authentication issues.

Issues Fixed

Came up due to confusion in #354

Checklist

• [x] You actually ran the code that you just wrote, especially if you did just "one last quick change".
• [x] ~~Comment-based help added/updated, including examples.~~
• [x] Static analysis is reporting back clean.
• [x] New/changed code adheres to our coding guidelines.
• [x] ~~Formatters were created for any new types being added.~~
• [x] ~~New/changed code continues to support the pipeline.~~
• [x] ~~Changes to the manifest file follow the manifest guidance.~~
• [x] ~~Unit tests were added/updated and are all passing. See testing guidelines. This includes making sure that all pipeline input variations have been covered.~~
• [x] ~~Relevant usage examples have been added/updated in USAGE.md.~~
• [x] ~~If desired, ensure your name is added to our Contributors list~~