Support prometheus metrics

[7ing]

certmanager_csi_certificate_request_expiration_timestamp_seconds certmanager_csi_certificate_request_ready_status
certmanager_csi_certificate_request_renewal_timestamp_seconds certmanager_csi_driver_issue_call_count
certmanager_csi_driver_issue_error_count
certmanager_csi_managed_certificate_count
certmanager_csi_managed_volume_count

fixes: #60

[cert-manager-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[cert-manager-prow]

Hi @7ing. Thanks for your PR.

I'm waiting for a cert-manager member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[erikgb]

/ok-to-test