Improve rollout status card and rollout controls

[data-sync-user]

Simplify the rollout status card and make its actions match the current rollout state.

• Remove links for Rollout Schedule, Preview and Testing Details from the sidebar
• Replace numbers with icons for Healthy or Warning
• When a rollout is disabled, do not continue showing actions such as Disable Rollout or Start Next Phase.
• Show the appropriate Cancel/approval flow instead
• Use a pause icon for Disable Rollout
• Add icons to relevant action buttons
• Use the Slack icon for Slack notification actions
• Use consistent outline style icons across all controls
• Fix the case where a newly created phase with 0% population cannot be started when that should be a valid state

┆Issue is synchronized with this Jira Task