[Backport][v1.78.x][Fix][Build] Move xds-protos templates to the new path (#41298)

Backport of #41297 to v1.78.x.
---
In #41261, templates weren't moved to the new path
`templates/py_xds_protos`, so they didn't render the updated version in
`py_xds_protos/grpc_version.py` correctly.

This resulted to fail with the following error:

```
Installing collected packages: xds-protos
Successfully installed xds-protos-1.77.0.dev0

+ /opt/python/cp313-cp313/bin/python -m build --no-isolation src/python/grpcio_csds
* Getting build dependencies for sdist...

ERROR Missing dependencies:
	xds-protos==1.78.0rc1
```

Note the difference in the expected and installed xds-protos version.

py_xds_protos/grpc_version.py

diff --git a/py_xds_protos/grpc_version.py b/py_xds_protos/grpc_version.py
index 4c168da..bbb6a44 100644
--- a/py_xds_protos/grpc_version.py
+++ b/py_xds_protos/grpc_version.py
@@ -14,5 +14,5 @@
 
 # AUTO-GENERATED FROM `$REPO_ROOT/templates/py_xds_protos/grpc_version.py.template`!!!
 
-VERSION = '1.77.0.dev0'
+VERSION = '1.78.0rc1'
 PROTOBUF_VERSION = '4.31.1'

templates/py_xds_protos/grpc_version.py.inja

diff --git a/templates/tools/distrib/python/xds_protos/grpc_version.py.inja b/templates/py_xds_protos/grpc_version.py.inja
similarity index 100%
rename from templates/tools/distrib/python/xds_protos/grpc_version.py.inja
rename to templates/py_xds_protos/grpc_version.py.inja

templates/py_xds_protos/python_version.py.inja

diff --git a/templates/tools/distrib/python/xds_protos/python_version.py.inja b/templates/py_xds_protos/python_version.py.inja
similarity index 100%
rename from templates/tools/distrib/python/xds_protos/python_version.py.inja
rename to templates/py_xds_protos/python_version.py.inja