Move health check to the backend (#2120)

This PR moves the health check to backend only leaving in the frontend
the functionality to test the dbconnector datasource.

Leaving the `dbconnector.testDataSource` should be fine since the
datasource types we allow for db connection with Zabbix already are
backend datasources, and so their health requests would go through the
backend.

Verified:
Clicking test and seeing a `health` request go out.

IMPORTANT: While testing this in the UI, I found a bug with the config
editor - whenever a change is made in the UI and tested, the changes
don't take effect (i.e. disabling trends, keeps `trends` set to `true`,
enabling db connection keep `dbConnectionEnabled` set to `false` and so
on.). Created a separate
[issue](https://github.com/orgs/grafana/projects/457/views/40?pane=issue&itemId=3627315751&issue=grafana%7Coss-big-tent-squad%7C132)
to fix this

Fixes https://github.com/grafana/oss-big-tent-squad/issues/124
Fixes https://github.com/grafana/grafana-zabbix/issues/2004

pkg/zabbix/testing.go

@@ -1,12 +1,31 @@
 package zabbix
 
 import (
+	"encoding/json"
+	"io"
+	"net/http"
+	"strings"
+	"testing"
+	"time"
+
 	"github.com/alexanderzobnin/grafana-zabbix/pkg/settings"
 	"github.com/alexanderzobnin/grafana-zabbix/pkg/zabbixapi"
 	"github.com/grafana/grafana-plugin-sdk-go/backend"
-	"time"
+	"github.com/stretchr/testify/require"
 )
 
+var BasicDatasourceInfo = &backend.DataSourceInstanceSettings{
+	ID:       1,
+	Name:     "TestDatasource",
+	URL:      "http://zabbix.org/zabbix",
+	JSONData: []byte(`{"username":"username", "password":"password", "cacheTTL":"10m"}`),
+}
+
+type ApiRequestPayload struct {
+	Method string                 `json:"method"`
+	Params map[string]interface{} `json:"params"`
+}
+
 func MockZabbixClient(dsInfo *backend.DataSourceInstanceSettings, body string, statusCode int) (*Zabbix, error) {
 	zabbixAPI, err := zabbixapi.MockZabbixAPI(body, statusCode)
 	if err != nil {
@@ -34,3 +53,50 @@ func MockZabbixClientResponse(client *Zabbix, body string, statusCode int) (*Zab
 
 	return client, nil
 }
+
+func NewZabbixClientWithHandler(t *testing.T, handler func(ApiRequestPayload) string) *Zabbix {
+	t.Helper()
+
+	httpClient := zabbixapi.NewTestClient(func(req *http.Request) *http.Response {
+		body, err := io.ReadAll(req.Body)
+		require.NoError(t, err)
+
+		var payload ApiRequestPayload
+		require.NoError(t, json.Unmarshal(body, &payload))
+
+		responseBody := handler(payload)
+		if responseBody == "" {
+			responseBody = `{"result":null}`
+		}
+
+		return &http.Response{
+			StatusCode: 200,
+			Body:       io.NopCloser(strings.NewReader(responseBody)),
+			Header:     make(http.Header),
+		}
+	})
+
+	dsSettings := *BasicDatasourceInfo
+	zabbixAPI, err := zabbixapi.New(dsSettings, httpClient)
+	require.NoError(t, err)
+
+	zabbixSettings := &settings.ZabbixDatasourceSettings{
+		Timeout: 10 * time.Second,
+	}
+	client, err := New(BasicDatasourceInfo, zabbixSettings, zabbixAPI)
+	require.NoError(t, err)
+
+	client.api.SetAuth("test")
+	client.version = 60
+
+	return client
+}
+
+func NewZabbixClientWithResponses(t *testing.T, responses map[string]string) *Zabbix {
+	return NewZabbixClientWithHandler(t, func(payload ApiRequestPayload) string {
+		if resp, ok := responses[payload.Method]; ok {
+			return resp
+		}
+		return `{"result":null}`
+	})
+}