Unifies SECURITY.md to point to the Zalando security form

[bocytko]

Unifies SECURITY.md to point to the Zalando security form.

Description

Motivation and Context

The majority of projects links to the security form. We still have some repositories that point to e-mail boxes.

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)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[whiskeysierra]

👍