docs: update usage-policy.md to suggest ticket system over email

[BlackAsLight]

This pull request changes the wording of the Report Violations section to suggest using the ticket system instead of sending an email. I am not sure if the wording is great or could be improved. There is also a few other spots that also suggest emailing still, but there isn't a clear button to open a ticket for it.

PR Checklist

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  And if changing dababase queries, be sure you have ran sqlx prepare
  and committed the changes in the .sqlx directory.

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[AugustinMauroy]

LGMT !