Add nfs_versions option for NFS protocol version selection

This commit introduces a new configuration option, `nfs_versions`,
to allow specifying the NFS protocol version used when mounting NFS
shares in Tempest tests. The option supports selecting specific
versions, such as NFSv3 or NFSv4, enabling compatibility with
environments where certain NFS versions are required.

- Option Name: `nfs_versions`
- Default: ["4", ] (NFSv4 is used by default)

This enhancement increases flexibility in testing scenarios with
NFS version dependencies.

Change-Id: I048d4e954329d2d4f28604a8bf02c615703ac43c
diff --git a/manila_tempest_tests/config.py b/manila_tempest_tests/config.py
index 03dfafb..decf2ac 100644
--- a/manila_tempest_tests/config.py
+++ b/manila_tempest_tests/config.py
@@ -108,6 +108,12 @@
     cfg.ListOpt("enable_ro_access_level_for_protocols",
                 default=["nfs", ],
                 help="List of protocols to run tests with ro access level."),
+    cfg.ListOpt("nfs_versions",
+                default=["4", ],
+                help="Specifies the NFS protocol version to use when mounting "
+                     "an NFS share. Set to '3' for NFSv3, and '4' or '4.1' "
+                     "for NFSv4. Leave it blank to use the default version."),
+
 
     # Capabilities
     cfg.StrOpt("capability_storage_protocol",