fix: make istio ingress gateway and control plane properties environment variables, to support external smcp, fixes RHOAIENG-19912

[dhirajsb]

Description

Add env variables in operator to allow connecting to an external smcp and ingress gateway.

How Has This Been Tested?

Tested manually by installing locally and applying local odh configuration generated with:

kustomize build config/overlays/odh

Generated odh overlay operator deployment uses env variables populated from odh operator configmap service-mesh-refs.
Verified that creating an MR with the new operator produces the following in the spec defaults:

,"gateway":{"controlPlane":"data-science-smcp","domain":"apps.rosa.dbokde-cluster.2rkm.p3.openshiftapps.com","istioIngress":"ingressgateway"}}

Note that the ingress gateway odh configmap property is optional, as an update is needed in ODH operator to pass that information to the MR operator in the future. The MR operator sets the value to the previous default ingressgateway.

Merge criteria:

• The commits and have meaningful messages; the author will squash them after approval or will ask to merge with squash.
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has manually tested the changes and verified that the changes work

[Al-Pragliola]

/lgtm

tested locally and everything seems to work, checked for backward compatibility