Update Pipeline Project README

The ironbank-pipeline README needs to be updated.

Areas that needs updating are:

Stage	Reason
Lint	The job's artifacts need to be noted
Documentation	Need to update section with new feature branch job and new script
Check CVEs	Remove reference to dccscr-whitelist as we use VAT as source of truth
Generate Allowlist	Stage is missing from project README

Acceptance Criteria

• All required updates have been made