Snapshots: Viewers can not create a Snapshot

[evictorero]

What is this feature?

This PR removes the ability to create snapshots for users without edit permissions on the dashboard addressing this old feature request.

Frontend

• Hide the Snapshot tab in the ShareModal for legacy and scene dashboards

Backend

• Add a permissions validation using a dashboard uid as scope
• Move payload binding to the API level
• Add changes to k8s snapshot API to support the same behavior

Use cases

• Users with viewer role cannot see the Snapshots tab or use the API
• Users with edit or admin role can create Snapshots for the particular Dashboard
• Users with viewer role but edit or admin permissions on a particular dashboard can create Snapshots for the particular Dashboard

Fixes #83529

Special notes for your reviewer:

Please check that:

• It works as expected from a user's perspective.
• If this is a pre-GA feature, it is behind a feature toggle.
• The docs are updated, and if this is a notable improvement, it's added to our What's New doc.