Allow raw api requests

[mblaschke-daimlertruck]

Is your feature request related to a problem?
Currently only prebuild APIs can be used with this client. Datasources also have own endpoints which are currently not useable.

Describe the solution you'd like
Add a function to send own API requests to Grafana

Describe alternatives you've considered
Forking is not a good idea

Additional context
eg. to trigger the subscription list of the grafana-azure-monitor-datasource using API /api/datasources/{uid}/resources/azuremonitor/subscriptions

[safaci2000]

I ended up doing this for some unsupported calls:

https://github.com/esnet/gdg/blob/master/internal/api/extended.go

Then, to use it:

var result []*models.UserOrgDTO

req := extended.getRequestBuilder().
	Path("api/user/orgs").
	ToJSON(&result).
	Method(http.MethodGet)

In this case i'm using the OpenAPI models but you can place it with anything you like...

All you really need is something like this:

	req := requests.URL(extended.grafanaCfg.URL)
	if extended.grafanaCfg.APIToken != "" {
		req.Header("Authorization", "Bearer "+extended.grafanaCfg.APIToken)
	} else {
		req.BasicAuth(extended.grafanaCfg.UserName, extended.grafanaCfg.Password)
	}

then use the req entity to build your call.