Document our slack spam policy and response procedure

Recently there was a message in the #random channel of slack that a community leader deemed to be spam.

I wanted to file this issue so that, when the infra committee is no longer on pause, we can ask around and document our guidelines (so people dont post spam in the first place) and procedures (how we will handle suspected spam).

Some things from this incident that can help inform this policy:
- When i first saw this message, I checked when the member sending it had joined slack (if they had joined very recently, i would likely have assumed it was a bot and that would have made an immediate ban more likely)
- i looked into the link that was sent (by visiting the company domain, not clicking the link) and finding an about page. The service seemed legit, even though it was pointing to some new AI service with a somewhat contradictory pitch.
- I was mostly waiting to see how it panned out and only felt confident acting when a community member with more tenure than myself joined the thread and called it spam based on their knowledge and experience moderating this community space

All of this is stuff that should be documented.

If infra team needs more of the details that im omitting from this public issue, see [this slack message](https://chaoss-workspace.slack.com/archives/C0AJG32PFND/p1786725301894489) (private channel, if you arent on the infra team, you likely wont have access).

Start by reviewing the incident details in this issue and the linked private Slack message, then consult the infra committee when it resumes. Done means the community’s spam-prevention guidelines and response procedure are agreed on and documented in the project’s documentation, though the target file or location is not specified.

Written by the indexing model from the issue text.