Backend plugins: Log wrapper args formatting (#20514)

Backend plugins is recommended to use hclog with json 
formatting to get proper log output in grafana server log.
Old hclog-wrapper.go that I deleted while back is still in 
the repo so deletes that.

pkg/plugins/backendplugin/log_wrapper_test.go

@@ -0,0 +1,29 @@
+package backendplugin
+
+import (
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLogWrapper(t *testing.T) {
+	tcs := []struct {
+		args           []interface{}
+		expectedResult []interface{}
+	}{
+		{args: []interface{}{}, expectedResult: []interface{}{}},
+		{args: []interface{}{"1", "2", "3"}, expectedResult: []interface{}{"1", "2", "3"}},
+		{args: []interface{}{"1", "2"}, expectedResult: []interface{}{"1", "2"}},
+		{args: []interface{}{"1", "2", "timestamp", time.Now()}, expectedResult: []interface{}{"1", "2"}},
+		{args: []interface{}{"1", "2", "timestamp", time.Now(), "3", "4"}, expectedResult: []interface{}{"1", "2", "3", "4"}},
+	}
+
+	for i, tc := range tcs {
+		t.Run(fmt.Sprintf("formatArgs testcase %d", i), func(t *testing.T) {
+			res := formatArgs(tc.args...)
+			assert.Exactly(t, tc.expectedResult, res)
+		})
+	}
+}