Check and fix adding file SECURITY.md

[ckunki]

This file is required to instruct customers reporting security issues in a safe and secure, yet unified way.

References

• Implementation in project-keeper
• File SECURITY.md in the PTB itself, added in PTB PR #62

Proposal

• Add the file to the cookie cutter templates
• Enhance PTB's nox session format:check to check if the file exists
• Enhance PTB's nox session format:fix to add the file if it doesn't exist

Alternatively, we could think about a more global and general sessions, e.g. project:check and project:fix.

Future enhancements (potentially in separate tickets)

• Enable projects to configure PTB to ignore if this file is missing.
• A generalized way to ignore specific PTB checks or fixes could be based on unique error codes and prefixes, see
  • error-reporting-python
  • project-keeper

[ArBridgeman]

Do we need to check in each CI run that the file is there?
Naively, I'd think we could just add it and maybe modify a tbx endpoint to ensure certain files are coordinated.