Code of Conduct refresh

The subject of a code of conduct has come up a few times, and this issue serves as a discussion thread. I hope that everyone will find the following statements uncontroversial:

1. Social spaces have rules, either stated or implied
2. Rules need to state clearly what is allowed and what is disallowed, so that people who may be interested in joining can determine if the culture is the right fit.
3. Rules need to be enforced
4. The Boost mailing lists already have rules
5. The rules for the mailing list are outdated
6. The rules for the mailing list are not particularly visible

There is value in refreshing the rules for the Boost mailing list, which are currently described here:

https://www.boost.org/community/policy.html

I think we should do the following:

* Update the rules to be relevant for 2024
* Make the rules visible on the sign-up and administration page for the mailing lists (at https://lists.boost.org)
* Consider renaming the rules to something other than "Boost Discussion Policy"
* Send a periodic announcement to the mailing lists reminding everyone of the rules. These could be timed to coincide with the releases (three times per year)