[Feat]: ability to add custom dashboard level node filter

[andrewm4894]

Problem

it would be very useful if i could apply a specific node filter to all charts in a custom dashboard.

right now i would need to individually select nodes from each chart which is very annoying if i have a lot of charts on a custom dashboard.

Description

ability to add a dashboard level node filter.

Importance

really want

Value proposition

1. make custom dashboard more usable

Proposed implementation

ability to "Add Filter" next to the existing "Add Chart" button. To begin that filter can just be a node filter but you could imagine different filter types potentially.

[hugovalente-pm]

this links directly to this https://github.com/netdata/netdata-cloud/issues/295