Query snippets do not adhere to permissions

[yanenok]

Issue Summary

Query Snippets are visible to and may be created and modified by any user regardless of their permissions. This is the same for the link in header and the snippets menu in settings.

Steps to Reproduce

1. Create a user in a group with no permissions.
2. That user can see the Query Snippets button in header and follow the link.
3. That user can see the Query Snippets tab in Settings and can create or modify snippets.

Technical details:

• Redash Version: v6.0.0