Implement CertGenerator

[fanminshi]

There are 5 cases that the CertGenerator impl needs to handle:

• case: Both TLS encryption key and cert and CA are in the cluster. ref:
  pkg/tlsutil: implement the case ca and key are in the cluster #412
• Testing above. ref: *: test the case when both app and CA TLS assets exist  #439
• case: TLS encryption key and cert are in the cluster but not the CA. ref: *: test the case where only the application TLS asset exists #444
• Testing above. ref: *: test the case where only the application TLS asset exists #444
• case: TLS encryption key and cert not in the cluster but the CA is. ref: *: implement and test the case where CA exists but App secret doesn't #446
• Testing above. ref: *: implement and test the case where CA exists but App secret doesn't #446
• case: None of the TLS encryption key and cert and the CA are in the cluster. ref: pkg/tlsutil: impl none of the CA and App TLS assets are found #450
• Testing above. ref: pkg/tlsutil: impl none of the CA and App TLS assets are found #450
• case: CA is passed in.
• Testing above

[openshift-bot]

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/lifecycle stale

[estroz]

/lifecycle frozen

[hasbro17]

The TLS cert generation pkg at pkg/tls is, for all intents and purposes, not supported anymore.
It was an early stage experimental effort to make it easier for operators to issue TLS certs to their applications but there are more complete solutions that exist like https://github.com/jetstack/cert-manager.

The SDK may support generating cert-manager manifests in the future.