[Feat]: Add a high contrast accessibility mode to the Netdata dashboard

[shyamvalsan]

Problem

Users with vision challenges find it difficult to use the Netdata UI

Description

This is especially applicable for grey text on grey background

Importance

must have

Value proposition

1. Ensuring Netdata (and observability) is accessible to everyone is a core principle of the company and we should prioritize this.

Proposed implementation

No response

[shyamvalsan]

User who shared feedback also suggested https://webaim.org/resources/contrastchecker/ as a reference.

[shyamvalsan]

@christophidesp for when you're back to take a look