Improve messaging and documentation around surplus schemata
Summary: Fixes T6795. Fixes T6813. We can give more tailored instructions for surplus schemata than we currently do, and provide more information on resolving them.
Test Plan:
- Ran storage adjust with just surplus schemata (friendly warning).
- Ran storage adjust with surplus schemata and other serious errors (more severe error).
- Read document.
Reviewers: btrahan, chad
Reviewed By: chad
Subscribers: epriestley
Maniphest Tasks: T6795, T6813
Differential Revision: https://secure.phabricator.com/D11054