Enable support for php

What does this MR do?

• Enables support for php.
• Pulls the php ruleset from sast-rules repository during buildtime.

What are the relevant issue numbers?

Migrate phpcs-security-audit coverage to Semgre... (gitlab-org/gitlab#364060 - closed) • Adam Cohen • 16.10

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 updated/added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer