Ask to use CalciteCrossClusterSearchIT when developing calcite-only commands

Signed-off-by: Yuanchun Shen <yuanchu@amazon.com>

Author: yuancu

docs/dev/ppl-commands.md

@@ -52,7 +52,7 @@ If you are working on contributing a new PPL command, please read this guide and
   - Add a test in `PPLQueryDataAnonymizerTest`
 
 - [ ] **Cross-cluster Tests (optional, nice to have):**
-  - Add a test in `CrossClusterSearchIT`
+  - Add a test in `CrossClusterSearchIT`, or in `CalciteCrossClusterSearchIT` if the command requires Calcite.
 
 - [ ] **User doc:**
   - Add a xxx.md under `docs/user/ppl/cmd` and link the new doc to `docs/user/ppl/index.md`