Update the Helm procedure to use oc-mirror for air-gapped OCP environments

[Fortune-Ndlovu]

IMPORTANT: Do Not Merge - To be merged by Docs Team Only

Version(s):

This PR updates the air-gapped installation documentation for Helm using oc-mirror. The updated docs now cover both partially disconnected and fully disconnected environments. These changes use oc-mirror tool to mirror Helm chart resources and generate an ImageContentSourcePolicy (ICSP) manifest for use in disconnected clusters. The key updates include:

• Partially Disconnected Environment:
  • Instructions to log in to the target registry, create an ImageSetConfiguration.yaml, and mirror resources directly using oc-mirror.
  • Guidance on locating and applying the generated imageContentSourcePolicy.yaml to the cluster.
  • Clear examples for deploying the Helm chart with the correct namespace and cluster router base configuration.
• Fully Disconnected Environment:
  • Instructions for generating a mirror archive file via oc-mirror, transferring it to the air-gapped environment, and mirroring resources from the archive.
  • Steps to locate and deploy the corresponding imageContentSourcePolicy.yaml and install the Helm chart using the archive.

Issue:
Related Issue: https://issues.redhat.com/browse/RHIDP-5351

Issue where the testing was verified: https://issues.redhat.com/browse/RHIDP-1723

Preview
Deep link: https://redhat-developer.github.io/red-hat-developers-documentation-rhdh/pr-868/install-rhdh-air-gapped/#proc-install-rhdh-airgapped-environment-ocp-helm_title-install-rhdh-air-grapped

[rhdh-bot]

Preview: https://redhat-developer.github.io/red-hat-developers-documentation-rhdh/pr-943/

[rm3l]

/cherry-pick release-1.5

(so we don't forget)

[openshift-cherrypick-robot]

@rm3l: once the present PR merges, I will cherry-pick it on top of release-1.5 in a new PR and assign it to you.

In response to this:

/cherry-pick release-1.5

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.

[linfraze]

This PR needs to be peer reviewed before it can be merged. Since I am the primary author of the content in the original PR, we need a different member of the docs team to review and approve it.

[Preeticp]

@Fortune-Ndlovu please ensure that all the review comments by our writer and others on the previous PR have been addressed in this one to avoid duplication of review effort. We will need to go through the standard review process but hopefully we can reduce the time taken.