Setup alert on an empty chart in metrics dashboard

Problem to solve

Users can define alerts directly from the charts in the metrics dashboard, however it is not possible today to configure alerts on empty charts

Proposal

From discussion in #36941 (comment 258861208), we should make the creation of an alert possible whenever it is technically possible to create an alert. In some of these scenarios, that would likely mean that the more options button is present on a chart empty state. Here is how that would look:

 

1. We will always show the ... dropdown menu. The dropdown will contain "Create alert", "Download CSV" and "Generate link to chart" options.
2. The items within the menu will be enabled or disabled based on these circumstances:

• The "Create alert" option will be enabled whenever the creation of an alert is possible (requires further investigation from an engineer to define when the creation of an alert is possible)
• The "Download CSV" option will be enabled when there's data to export and disabled when there's no data. In case the engineer decides to break it down into a separate issue, we can keep the "Download CSV" enabled at all times as part of this issue and address the conditional enabled/ disabled state in a follow-up issue.
• The "Generate link to chart" option will be enabled at all times.