docs: add note in CRD that using Routes with external certificates in TLS Secrets is Technical Preview in OCP [RHDHBUGS-45]

[rm3l]

Description

This is a follow-up to https://issues.redhat.com/browse/RHDHBUGS-45

Right now, using the Operator, a user can reference an external certificate as a Secret in their CR, like so:

spec: 
  application: 
    route: 
      enabled: true
      host: my-rhdh.apps.example.com
      tls: 
        externalCertificateSecretName: my-rhdh-tls-cert

However, as depicted in https://docs.openshift.com/container-platform/4.16/networking/routes/secured-routes.html#nw-ingress-route-secret-load-external-cert_secured-routes, Securing route with external certificates in TLS secrets is a Technology Preview feature only. As such, it requires enabling the RouteExternalCertificate Feature Gate in OpenShift.

This updates the doc about the spec.application.route.tls.externalCertificateSecretName CRD field accordingly.

Note that there is a dedicated issue for the product docs team to call this out: https://issues.redhat.com/browse/RHIDP-3292

Which issue(s) does this PR fix or relate to

• Relates to https://issues.redhat.com/browse/RHDHBUGS-45
• Relates to https://issues.redhat.com/browse/RHIDP-3292

PR acceptance criteria

• Tests
• Documentation
• If the bundle manifests have been updated, make sure to review the rhdh-operator.csv.yaml file accordingly

How to test changes / Special notes to the reviewer

Preview of how this looks like in the OCP web console:

[sonarcloud]

Quality Gate failed

Failed conditions
16.0% Duplication on New Code (required ≤ 3%)

See analysis details on SonarCloud

[rm3l]

/cc @gazarenkov

[github-actions]

PR images are available:

1. https://quay.io/janus-idp/operator:0.3.0-pr-413-2177f54
2. https://quay.io/janus-idp/operator-bundle:0.3.0-pr-413-2177f54
3. https://quay.io/janus-idp/operator-catalog:0.3.0-pr-413-2177f54

[openshift-ci]

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[rm3l]

/override "SonarCloud Code Analysis"

Duplication here is a result of having the same doc generated in the bundle manifests.

[openshift-ci]

@rm3l: Overrode contexts on behalf of rm3l: SonarCloud Code Analysis

In response to this:

/override "SonarCloud Code Analysis"

Duplication here is a result of having the same doc generated in the bundle manifests.

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