Allow for custom disk size and type when using VertexAI Step Operator

[strickvl]

Updated our step operator to allow for custom disk sizes when using VertexAI step operator.

Pre-requisites

Please ensure you have done the following:

• I have read the CONTRIBUTING.md document.
• If my change requires a change to docs, I have updated the documentation accordingly.
• If I have added an integration, I have updated the integrations table and the corresponding website section.
• I have added tests to cover my changes.
• I have based my new branch on develop and the open PR is targeting develop. If your branch wasn't based on develop read Contribution guide on rebasing branch to develop.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Other (add details above)

[avishniakov]

All good, but can we test it somehow? Or we don't do vertex tests atm?

[strickvl]

@avishniakov we don't do any tests on deployed infrastructure, but I have tested it to ensure it works.

[github-actions]

E2E template updates in examples/e2e have been pushed.