Enable Exemplar Storage in Mimir

Motivation

Exemplars allow SREs to easily correlate anomalous metrics readings with traces that exemplify the behavior observed. This allows for easier root-cause analysis and remediation. By default, Mimir only stores exemplars in memory in a circular buffer. This means that as new exemplars are received, old exemplars are evicted and trace correlation for older traces is no longer possible. Enabling storage for the exemplars allows Mimir to provide historical trace correlation.

Acceptance Criteria

• Mimir must be configured to store exemplars
• Mimir may be configured to accept out-of-order exemplars