Reorder license scanning-related topics in docs navigation
Reorder and edit several docs navigation items about license scanning.
- Move "License scanning of CycloneDX files" to near the top as it's the recommended method.
- Rename "License check rules" entry to match the docs' title, which uses "policies".
- Remove "Rake task" from "SPDX license list import" because that's an implementation detail and unnecessary in the docs navigation.
Note: In future I plan to abbreviate the CycloneDX entry to "License scanning" but I first want to consult the relevant PM.
Edited by Russell Dickenson