Time series deletion API for block storage

[ilangofman]

Currently, Cortex only implements a time series deletion API for chunk storage. We would like to have the same functionality with blocks storage. Ideally, the API for deleting series should be the same as currently in Prometheus and in Cortex with chunk storage.

Motivation:

• Confidential or accidental data might have been incorrectly pushed and needs to be removed.
• GDPR regulations require data to be eventually deleted

I am currently working on the design doc, and will link it soon.

[stale]

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