Failed to upgrade legacy queries

[DifferentialOrange]

@opomuc reported that installing Tarantool dashboard on Grafana 9.2.2 failed with

Failed to upgrade legacy queries Datasource ${DS_PROMETHEUS} was not found

but I failed to reproduce this one.

[opomuc]

This happens when using Dashboard provisioning and creating dashboards from files on disk.

[DifferentialOrange]

The reason why this error was raised is that the dashboard was imported through Grafana provisioning: exporting a raw json fails since there is no way to fill __inputs import datasource variable.

It seems that reworking import variables to be similar to what used in node exported dashboard (see #185) should solve this one. It is also may be helpful to rework datasource later (not until we deprecate 8.x), see #189 .

For now, this ticket is closed in favor of #185 . The solution for #185 is expected to solve provisioning import too.