Support global_prefix on Grafana import

[Matthias-Beck]

Is your feature request related to a problem? Please describe.
Support exporter global_prefix for Grafana dashboard import. If a prefix is defined today, all queries on the dashboards have to be updated manually

Describe the solution you'd like
While importing the dashboards via the Grafana tool, the exporter section should be checked for global_prefix entries.

Describe alternatives you've considered
Add a command parameter (e.g. --db-prefix) to the Grafana tool like the --datasource parameter for naming the prefix and updating the queries in the dashboards.

[vgratian]

Hi Matthias, good point.

This issue is loosely related to #22

[cgrinds]

Verified dashboard queries are rewritten on import

bin/harvest --version
harvest version 21.08.0-1 (commit 956ebfa) (build date 2021-08-25T11:36:10-0400) linux/amd64

bin/grafana import --directory grafana/dashboards/ --folder h2 --prefix foople

using API token from config
connected to Grafana server (version: 8.1.2)
created Grafana folder [h2] - OK
preparing to import 12 dashboards...
OK - imported [harvest_dashboard_aggregate.json]
OK - imported [harvest_dashboard_cluster.json]
OK - imported [harvest_dashboard_disk.json]
OK - imported [harvest_dashboard_metadata.json]
OK - imported [harvest_dashboard_network.json]
OK - imported [harvest_dashboard_node.json]
OK - imported [harvest_dashboard_nvme_fc.json]
OK - imported [harvest_dashboard_shelf.json]
OK - imported [harvest_dashboard_snapmirror.json]
OK - imported [harvest_dashboard_svm.json]
OK - imported [harvest_dashboard_volume.json]

Then went to dashboards and confirmed queries are prefixed with foople