Data Source Proxy: Migrate proxy to its own service and make more extensible (#31927)

* datasource proxy extensions

* revert normalresponse extensions

* data proxy service impl

* lint

* api datasource proxy method

* moves datasource proxy tests into correct new pkg

pkg/services/datasourceproxy/datasourceproxy_test.go

@@ -0,0 +1,34 @@
+package datasourceproxy
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDataProxy(t *testing.T) {
+	t.Run("extractProxyPath", func(t *testing.T) {
+		testCases := []struct {
+			originalRawPath string
+			exp             string
+		}{
+			{
+				"/api/datasources/proxy/1",
+				"",
+			},
+			{
+				"/api/datasources/proxy/1/some/thing",
+				"some/thing",
+			},
+			{
+				"/api/datasources/proxy/54/api/services/afsd%2Fafsd/operations",
+				"api/services/afsd%2Fafsd/operations",
+			},
+		}
+		for _, tc := range testCases {
+			t.Run("Given raw path, should extract expected proxy path", func(t *testing.T) {
+				assert.Equal(t, tc.exp, extractProxyPath(tc.originalRawPath))
+			})
+		}
+	})
+}