[DRAFT] Removing decomissioned certificates from the metrics

[anispate]

As part of the bug OSD-14653, we will be trying to delete the decom certs from the UpdateCertValidDuration metrics.

Currently, as shown in this link (https://grafana.app-sre.devshift.net/explore?schemaVersion=1&panes=%7B%22x7t%22:%7B%22datasource%22:%22P3D303D298AFF784A%22,%22queries%22:%5B%7B%22refId%22:%22A%22,%22expr%22:%22certman_operator_certificate_valid_duration_days%20%3C%2045%22,%22range%22:true,%22instant%22:true,%22datasource%22:%7B%22type%22:%22prometheus%22,%22uid%22:%22P3D303D298AFF784A%22%7D,%22editorMode%22:%22code%22,%22legendFormat%22:%22__auto%22,%22useBackend%22:false,%22disableTextWrap%22:false,%22fullMetaSearch%22:false,%22includeNullMetadata%22:true%7D%5D,%22range%22:%7B%22from%22:%22now-1h%22,%22to%22:%22now%22%7D%7D%7D&orgId=1) it is showing us all the certificates which are decommissioned