Testdata: Rename package to circumvent convention in go (#19409)

Before this change the tests for test datasource was not run.

pkg/tsdb/testdatasource/utils.go

@@ -0,0 +1,22 @@
+package testdatasource
+
+import (
+	"math/rand"
+	"time"
+)
+
+type randomStringProvider struct {
+	r    *rand.Rand
+	data []string
+}
+
+func newRandomStringProvider(data []string) *randomStringProvider {
+	return &randomStringProvider{
+		r:    rand.New(rand.NewSource(time.Now().UnixNano())),
+		data: data,
+	}
+}
+
+func (p *randomStringProvider) Next() string {
+	return p.data[p.r.Int31n(int32(len(p.data)))]
+}