🧹 [Maintenance]: Centralize community policies (#47)

## Summary

New module repositories inherit the centrally maintained support,
security, and code-of-conduct policies from PSModule/.github instead of
shipping duplicate copies.

## Technical details

- Remove SUPPORT.md, SECURITY.md, and CODE_OF_CONDUCT.md from the
template.
- Keep policy ownership in the public organization .github repository.
- The central policy update, including Contributor Covenant 3.0, is
delivered separately in PSModule/.github.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: MariusStorhaug