Deprecate and stop processing `message` field in `VulnerabilityCreate` GraphQL mutation

Why are we doing this work?

In !116538 (merged) we removed support for security report JSON schema version 14-x-x. This, in turn, removed the message field. Unfortunately, we forgot to deprecate the message field on the VulnerabilityCreate GraphQL mutation which can be used to manually create Vulnerabilities.

Implementation plan

1. Mark message argument in VulnerabilityCreate GraphQL mutation as deprecated
2. Don't process the message arugment
3. Mark message field in Vulnerability GraphQL type as deprecated