[OneDiscover][Extension] DataTable Custom Cell Popover Content

[kertal]

📓 Summary:

By default, Discover's data table shows the cell content in a popover, when expanded:

Discover's contextual awareness framework should provide an extension point allowing to register additional cell popover content for defined fields. Here's an example showing host metrics utilizing basic area chart:

✔️Acceptance criteria:

• Discover's contextual awareness framework should be extended by an extension point allowing to register additional cell actions popover content of Discover's data table for specific
• It should be used in an example profile
• Apart from unit tests it should be covered by functional tests using the example profile

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)