Independence for embed timewindow scroll

What does this MR do?

Addresses the issue described in #31004 (closed)

1. Don't link hover/zoom on charts from different dashboards, or for single embeds
2. Add unique groupId in case multiple different dashboards are embedded

groupId is used to connect chart.vue in gitlab-ui

Screenshots

Clip showing 2 charts from a Dashboard being moved while staying syncronised, followed by some individual charts that are moved independently.

Screen_Recording_2019-10-14_at_9.50.43_pm

Dashboard charts are still synced, behavior is unchanged

Screen_Recording_2019-10-17_at_10.52.36_am

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides