relax the CRD certificates availability requirement

[wasaga]

Is your feature request related to a problem? Please describe.

Currently, IC won't start if the certificates secrets referenced in the CRD do not exist.

That creates an issue for the authenticate endpoint if an HTTP-01 challenge is required by the cert-manager to acquire the certificate.

Describe the solution you'd like

Skips certs that do not exist, and just do warning in the CRD status / events.

The cert-manager would be able then to use Pomerium to solve HTTP-01 challenge for the authenticate certificate that Pomerium would pick up once available.

Describe alternatives you've considered

Explain any additional use-cases

If there are any use-cases that would help us understand the use/need/value please share them as they can help us decide on acceptance and prioritization.

Additional context

Add any other context or screenshots about the feature request here.

[desimone]

We can approach this with code or with docs.