Rename common report formatter

What does this MR do?

this merge request renames common_report_formatter to security_report_formatter by renaming the constant, references to it and renaming some files. the reason for this is that we're moving away from this terminology and would like this to be reflected in dast.

i opted to do this in a single merge request but i'm open to hearing feedback about different ways i could have approached this to avoid disruption for other developers.

What are the relevant issue numbers?

gitlab-org/gitlab#214233 (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
  • Job definition example
  • Vendored CI Templates (also in CE)
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer