Temporary ban users

Eclipse Foundation report that consequences of Unacceptable Behavior escalate as follow:

• A warning.
• A temporary 30-day ban from all Eclipse Foundation channels.
• A permanent ban from all Eclipse Foundation channels.

ref: https://www.eclipse.org/org/documents/communication-channel-guidelines/

Mjolnir bot moderator is not able to ban users temporary. Only an unban manual action after a delay is possible.

Open issue Temporary ban cmd to prevent gigantic banlists and to moderate proportionally #318