Got "Failed to upgrade legacy queries Datasource $ds was not found" in
Grafana on operator dashboard.
It's datasource variable was incorrectly named `datasource`.
Also made the rest of the dashboards have homogeneous datasource-variable
names and selections, matching vmagent dashboard.
* some unexpected DS UIDs were removed;
* replace `$instance.*` filter with `$instance` since we respect
the instance port anyway;
* remove predefined datasource for `clusterbytenant`
in favour of datasource variable `ds`.
Signed-off-by: hagen1778 <roman@victoriametrics.com>
Signed-off-by: hagen1778 <roman@victoriametrics.com>
