Add Multitenacy examples to Datasource docs

[tiny-pangolin]

Describe the bug

The datasource does not show how to add the AccountID and ProjectID headers to specify which tenant to add as datasource. At a minimum it should have these values commented out in the example provisioning config and Ideally have a brief explanation and reference to the multitenancy docs in Victorialogs along with a screenshot on how to do this in the GUI

To Reproduce

1. go to https://docs.victoriametrics.com/victorialogs/victorialogs-datasource/#grafana-provisioning
2. follow instructions for adding in a data source using the provisioning API
3. notice that * returns no results or the wrong results, since logs were sent to a different tenant.

Version

latest

Logs

No response

Screenshots

No response

Used command-line flags

No response

Additional information

No response