[docs] clarify guidelines for new contributors

This adds the Contributor Covenant 1.2 from the previous guidelines,
as well as a github workaround for new contributors who run into the
0xacab 1-repo limit (or similar issues). Replaces a 404 link in the
leap-commit-template, and adds a reminders to anonymize logs for
testers.

- Documentation: #9138

Signed-off-by: Ruben Pollan <meskio@sindominio.net>