Replace help buttons and version in the help footer with the ones provided by Grafana

[jdbaldry]

Before (in Ops):

• Uses static buttons bundled in the plugin
• Renders a fake modal for keyboard shortcuts
• Uses an approximate version string which differs from the one rendered for users in Grafana Cloud
• Uses non-standard link button components with modified hover behavior

After (local dev):

• Renders the help menu items provided by Grafana
• Renders the full keyboard shortcuts modal
• Uses the help menu version string
• Uses standard Grafana LinkButton components

[jdbaldry]

I need to work out how I can satisfy the @grafana/scenes runtime dependency. Will take a look and see if there's some guidance on that in the scenes source.