CI: add a scheduled job that always succeeds

Sits on top of !29 (merged), only the last commit matters.

This is part of the damspam sanitize-profiles integration: we will schedule this pipeline as a regular job and it does nothing but succeed. But in doing so it will fire off a pipeline event to the webhooks which hookiedookie can then use to run damspam sanitize-profiles with the required auths.

This way the secrets stay secret (only inside the hookiedookie deployment) but we don't need to configure a cron job on the cluster.

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• scheduled pipeline is inactive, re-enable when merging
• merge fdo-bots!2 (merged) for this to have any effect
• enable pipeline events in the damspam webhook