bert for zero shot classification crashes on sentence basis

[ahmedlone127]

Description

This change modifies BertForZeroShotClassification by adding a method for padding with zeros all required arrays inside a batch to ensure all of them have the same length.

How Has This Been Tested?

ran local unit tests that were previously failing

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Code improvements with no or little impact
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING page.
• I have added tests to cover my changes.
• All new and existing tests passed.