Make environment variables consistent

For better consistency

Rename DAST_AUTH_EXCLUDE_URLS to DAST_EXCLUDE_URLS since its not exclusively related to "AUTH"

• Update the documentation to refer to the new variable
• Continue to support the old variable in the code, but remove it from the documentation

Use CI_SERVER_VERSION_MAJOR to check the version of GitLab so that DAST_AUTH_EXCLUDE_URLS can be removed after %14.0

Implementation Plan

• Add DAST_EXCLUDE_URLS to DAST gitlab-org/security-products/dast!367 (merged)
• Add DAST_EXCLUDE_URLS to DAST documentation !51289 (merged)
• Deprecate DAST_AUTH_EXCLUDE_URLS in documentation (How do we do this?)
• Stop DAST_AUTH_EXCLUDE_URLS and AUTH_EXCLUDE_URLS working after %14.0 (before working on this make sure gitlab-org/security-products/dast!373 (merged) is resolved and use the same method)