Fix buffer overflow on large files

What does this MR do?

Replaces !6 (closed)

Replace bufio.Scanner usage with bufio.Reader to handle large file buffers exceeding 64kb.

❯ time docker run --rm --volume /Users/theoretick/code/tmp/gitlab-ee/:/tmp/project --env CI_PROJECT_DIR=/tmp/project analyzer /analyzer run

real	7m52.678s
user	0m0.047s
sys	0m0.026s

This also uncovered an inconsistency introduced with !5 (merged) where the rulename was incorrect: RKCS8 should be PKCS8

No description for Gitleaks rule PKCS8, please open an issue on https://gitlab.com/gitlab-org/gitlab-ee/issues

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/10281

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
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer