Impulse: Different color plates for different severities of firing alerts

[nixargh]

Hi, team.
First of all, thank you for your work on Impulse!

From my POV it's convenient to have color difference between alert of various severities (works at Slack & Muttermost). For example we use three of them: info=blue, warning=yellow, critical=red. We use severity label to choose the one at Alertmanager template:

  slack.template: |
  ¦ {{/* Color of the alert*/}}
  ¦ {{ define "slack_color" -}}
  ¦ ¦ ¦ {{ if eq .Status "firing" -}}
  ¦ ¦ ¦ ¦ ¦ {{ if eq .CommonLabels.severity "warning" -}}
  ¦ ¦ ¦ ¦ ¦ ¦ ¦ warning
  ¦ ¦ ¦ ¦ ¦ {{- else if eq .CommonLabels.severity "critical" -}}
  ¦ ¦ ¦ ¦ ¦ ¦ ¦ danger
  ¦ ¦ ¦ ¦ ¦ {{- else -}}
  ¦ ¦ ¦ ¦ ¦ ¦ ¦ #439FE0
  ¦ ¦ ¦ ¦ ¦ {{- end -}}
  ¦ ¦ ¦ {{ else -}}
  ¦ ¦ ¦ good
  ¦ ¦ ¦ {{- end }}
  ¦ {{- end }}

But for the time being Impulse has a hardcoded set of colors:

status_colors = {
    'firing': '#f61f1f',
    'unknown': '#c1a300',
    'resolved': '#56c15e',
    'closed': '#969696',
}

I think there are many possible solutions. For example include severities to colors map, like this:

status_colors = {
    'firing': {
        'default': '#f61f1f',
        'info': '#jjjjjj',
        'warning': '#ssssss',
        'critical': '#dddddd',
    }
    'unknown': '#c1a300',
    'resolved': '#56c15e',
    'closed': '#969696',
}

And use non-default if severity detected. I haven't read the code well enough to get how severity might be delivered to that level but shouldn't be very difficult...

I understand the point to do backward compatible changes, so it would be nice to have a switch for this feature. And possibility to remap colors as well :)