Add the ability to override the Edge endpoint checking interval at the endpoint level

[deviantony]

Introduce a new endpoint property to override the default specified in the Settings.

This property should be available in the endpoint creation and endpoint details view for an Edge endpoint.

UX/UI: provide a dropdown allowing to select one of the following options:

• Use default interval
• 5 seconds
• 10 seconds
• 30 seconds
• 5 minutes
• 1 hour
• 1 day

Default selected option should be "use default interval".

In the Settings, rename the "Edge agent poll frequency settings" to "Edge agent default poll frequency" update the tooltip to "Interval used by an Edge agent to check in with the Portainer instance. Affects Edge endpoint management and Edge compute features".