Add rules for DigitalOcean prefixed tokens

What does this MR do?

Adds new detection rules for DigitalOcean PATs, Access tokens, and refresh tokens. Back in April, DigitalOcean updated their tokens to have distinct prefixes:

• dop_v1_ for PATs.
• doo_v1_ for OAuth access tokens.
• dor_v1_ for OAuth refresh tokens.

I have also created a PR zricethezav/gitleaks to add the same rules there.

What are the relevant issue numbers?

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