[Feat]: Reachability notifications Enhancements

[sashwathn]

Problem

The reachability notifications can be spammy when there is a network issue between Netdata agent (parent or child) and the cloud. We need to find a solution to make it configurable and group the notifications.

Description

Netdata needs to support following functionality on the reachability notifications to reduce the spam:

• User Configurable timeouts for reachability notifications.
• In a scenario where the child nodes are not connected to cloud (directly) and are connected via a parent (or a parent cluster), If the connectivity between the parent (or parent cluster) and the cloud is down, coalesce / group the notifications (for the parent and all its children)
• If one of the parents is connected to the cloud, reachability notifications should not be triggered for all the children (I think this is already supported but good to check).

cc: @car12o @ktsaou @ralphm @stelfrag @Ferroin

Importance

must have

Value proposition

1. Reduces spammy notifications
2. Provides more control to the user based on their knowledge of their own network.

Proposed implementation

• User Configurable timeouts for reachability notifications.
• In a scenario where the child nodes are not connected to cloud (directly) and are connected via a parent (or a parent cluster), If the connectivity between the parent (or parent cluster) and the cloud is down, coalesce / group the notifications (for the parent and all its children)