feat: Allow finalizer cleanup when realm is already deleted

[andser91]

Pull Request Template

Description

This PR fixes an issue where deleting a custom resource (e.g., KeycloakClient, KeycloakGroup, etc.) that references a KeycloakRealm CR which has already been deleted results in a permanent reconciliation failure.

Currently, when a child resource is deleted, the controller tries to instantiate a Keycloak client by fetching the corresponding KeycloakRealm CR. If the realm CR has already been deleted, the controller throws a NotFound error, and the resource remains stuck in a terminating state because the finalizer is never removed.

This patch ensures that if the referenced realm no longer exists, the finalizer is still properly removed, allowing the resource to be garbage collected.

Fixes #173

Type of change

• [✓ ] Enhancement (non-breaking change which improves an existing feature or documentation)

How Has This Been Tested?

• Deployed the operator in a development environment with CAPI-generated clusters and Keycloak running.
• Created a KeycloakRealm and a related KeycloakClient.
• Deleted the KeycloakRealm before the KeycloakClient.
• Verified that the KeycloakClient finalizer was correctly removed, and the resource was deleted without manual intervention.
• Added test case in keycloakclient_controller_integration_test

Checklist:

• [✓] I have performed a self-review of my code
• [✓] I have commented on my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• [✓] My changes generate no new warnings
• [✓] I have added tests that prove my fix is effective or that my feature works
• [✓] New and existing unit tests pass locally with my changes
• [✓] Pull Request contains one commit. I squash my commits.

[zmotso]

@andser91 Thank you for your contribution.
Your change can improve cleaning resources.
Please fix the comments.
Change commit message to: feat: Allow finalizer cleanup when realm is already deleted (#173)
Make sure you run make lint.

[zmotso]

@SergK @MykolaMarusenko Looks good, let's merge this PR.

[SergK]

@andser91 Thank you