Grafana dashboards: make timezone configurable

[ricsanfre]

Enhancement Description

Make timezone specified in dashboards configurable when deploying them.

In all dashboards in json format timezone is specified using timezone key

{
.....
  "timezone": "<timezone>",
  "title": "<dashboard_tittle>",
  "uid": "<dasboard_uid>",
  "version": 0,
  "description": "<dashboard_description>"
}

This key can be UTC ("utc") or local timezone ("Europe/Madrid").

Changes to be implemented

1. Use ansible variable (defaultGrafanaDashboardsTimezone) to specify the Timezone to be used in dashboards, and transform current json dashboards into jinja templates to use that variable.

2. kube-prometheus-stack chart uses a value grafana.defaultDashboardsTimezone to configure timezone in all dashboards it deploys. Deploy kube-prometheus-stack setting this value using the ansible variable defaultGrafanaDashboardsTimezone