🐛 (helm/v2-alpha): Support custom container names and fix templating bugs

[AlirezaPourchali]

Fixes #5449

This PR adds support for custom container names via kubectl.kubernetes.io/default-container annotation and fixes two critical bugs found during testing.

Background

PR #5452 attempted to add this feature but has implementation issues that prevent it from working correctly. This PR provides a complete working solution.

Changes

New Feature:

• Added getDefaultContainerName() function to read kubectl.kubernetes.io/default-container annotation
• Falls back to "manager" for backward compatibility when annotation is missing

Bug Fix 1: Container names were being incorrectly templated

• substituteResourceNamesWithPrefix() was converting container names to Helm templates like {{ include "chart.resourceName" ... }}
• Container names are internal pod identifiers and should remain literal, not templated like cluster-wide resource names
• Root cause: Container names with dashes (e.g., osiris-manager, controller-test) match the same regex pattern project-prefix-* intended for resource names like project-webhook-service
• Fixed by detecting container context (looking backward for containers:) and excluding them from templating

Bug Fix 2: Image templating failed with custom container names

• Order-of-operations issue: substituteResourceNamesWithPrefix runs before templateImageReference
• When container name gets templated first, the image regex no longer matches the literal container name
• Fixed by modifying all image-related functions (templateImageReference, templateEnvironmentVariables, templateResources, templateContainerSecurityContext, templateControllerManagerArgs) to check for both literal and templated container names

Testing

• ✅ Unit tests added for custom container name support
• ✅ Verified with custom container name controller-test
• ✅ Backward compatibility maintained with default manager container name
• ✅ All existing tests pass

Example

Projects can now use any container name:

metadata:
  annotations:
    kubectl.kubernetes.io/default-container: my-custom-controller
spec:
  containers:
  - name: my-custom-controller  # Stays literal, not templated
    image: controller:latest     # Gets templated correctly

[k8s-ci-robot]

Hi @AlirezaPourchali. Thanks for your PR.

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[camilamacedo86]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AlirezaPourchali, camilamacedo86

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[camilamacedo86]

/ok-to-test