[controller] Remove subDir parameter from NFSStorageClass

[AleksZimin]

Description

This PR removes the subDir parameter from the NFSStorageClass configuration and related code. This change aims to simplify the configuration process and reduce the likelihood of configuration errors.

Why do we need it, and what problem does it solve?

Removing the subDir parameter helps streamline the configuration of NFSStorageClass, making it easier for users to set up and manage their storage classes. By eliminating this parameter, we reduce the complexity of the configuration, thereby minimizing the chances of misconfigurations and improving the overall user experience.

What is the expected result?

• Simplified NFSStorageClass configuration without the subDir parameter.
• Reduced risk of configuration errors.

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.