Use accent colors for clusters

[joaquimrocha]

Since we support multiple clusters, a nice way to quickly identify them (besides the name) is to assign them a different color. We shall call this the cluster's accent color as it will be reflected in a few parts of the dashboard.

We understand this is not an accessible option for color-blind users, but that should be covered by #14 .

This feature also requires having a settings view (#16).

Acceptance Criteria:

• [ ] Allow the user to select a color for each configured cluster
• [ ] Use this color in the cluster's icon (if not custom) and other elements in the UI (TBD)