docs(security findings): Update doc screenshots and minimum versions

Description

Update Changelog and Docs Screenshots for Security Findings

• Screen record new gif for https://marketplace.visualstudio.com/items?itemName=GitLab.gitlab-workflow#security-findings and update readme
• Add mention of minimum supported gitlab version
• Add mention that it is Ultimate only

Screenshots

Before:

https://marketplace.visualstudio.com/items?itemName=GitLab.gitlab-workflow

After: (markdown preview, final version styling looks like the production link above)

Related Issues

Resolves #1247 (closed)

How has this been tested?

Screenshots (if appropriate)

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)
• Documentation
• Chore (Related to CI or Packaging to platforms)
• Test gap

Closes #1247 (closed)