fix(insights): Improve experience of restricted insights

[Twixes]

Problem

Addresses #8460 (comment) (not the whole issue, just that comment).

Changes

Three commits, three changes:

1. Don't show redundant lock icon on insight description – one lock, on the insight name aka page title, is enough
2. Allow playing with insight settings in view mode (read-only) – this is the main issue
3. Show lock icon in dashboards list – previously it wasn't possible to tell if you can edit a dashboard just looking at the list

[pauldambra]

LGTM