Keycloak 26 enable internal connection

[rickysway]

What this PR does / why we need it:
As of Keycloak 25 onwards, with the move to Hostname V2, for internal cluster Pod to Service communication you need to enable backchannelDynamic (effectively adding env var KC_HOSTNAME_BACKCHANNEL_DYNAMIC: 'true' to Keycloak), we opt for setting the env as a customer could potentially installed Keycloak 24 in another namespace after this installation, which will break their Keycloak 26 installation if we relied on backchannelDynamic due to the change of CRD
https://www.keycloak.org/server/hostname#_utilizing_an_internal_url_for_communication_among_clients

According to Keycloak Hostname V2 docs when spec.hostname.backchannelDynamic: true the hostname needs to be a URL and not just hostname, so adding https:// to the start of the hostname value
https://www.keycloak.org/server/hostname#_validations

Which issue(s) this PR fixes:
Fixes https://github.ibm.com/IBMPrivateCloud/roadmap/issues/65922

Special notes for your reviewer:
Unsure if the below section "backport" is needed

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[ibm-ci-bot]

Welcome @rickysway! It looks like this is your first PR to IBM/ibm-common-service-operator 🎉

[ibm-ci-bot]

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[rickysway]

This does not work on Keycloak 22/24. Noting the url becomes https://https//........
This works on Keycloak 26 however

[YCShen1010]

Hello @rickysway, I think we could directly define .spec.additionalOptions in the Keycloak CR to enable KC_HOSTNAME_BACKCHANNEL_DYNAMIC equals to true instead, and then it will be present in the env in pod yaml.
Doc link: https://www.keycloak.org/server/all-config#category-hostname_v2
example:

data:
    spec:
    ...
    additionalOptions:                          <----- newly added
      - name: hostname-backchannel-dynamic
        value: "true"
    ...
    ...
    proxy:
      headers: xforwarded
    features:
      enabled:
        - token-exchange
        - admin-fine-grained-authz

When it is enabled as true, it requires https:// as a prefix for the hostname. We are going to enhance the ODLM templating logic to handle this, and I could open a new PR with this update later.
Thank you for pointing out these changes to us.