Do not require colon and space in cwe field

What does this MR do?

Part 2 of an MR to allow rule authors to use the shortDescription field and not require the CWE field to contain title information, or the characters required to parse the title out.

What are the relevant issue numbers?

gitlab-org/gitlab#398500 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Ensure the report version matches the equivalent schema version
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer