feat: generalize container tool usage in Makefile template

[rhuss]

Description of the change:
This PR generalizes the container tool usage in the bundle build target to respect the CONTAINER_TOOL variable. The change replaces the hardcoded docker command with $(CONTAINER_TOOL) in the bundle-build target of the Makefile template, making it consistent with other container-related targets in the operator-sdk.

Motivation for the change:
Currently, the bundle build target hardcodes the use of docker as the container tool, which is inconsistent with other parts of the operator-sdk that respect the CONTAINER_TOOL variable. This change:

1. Makes the bundle build process more flexible by allowing users to use alternative container tools like podman
2. Maintains consistency with the rest of the operator-sdk tooling
3. Follows the existing pattern used in other container-related targets

Checklist

If the pull request includes user-facing changes, extra documentation is required:

• Add a new changelog fragment in changelog/fragments (see changelog/fragments/00-template.yaml)
• Add or update relevant sections of the docs website in website/content/en/docs

[camilamacedo86]

Hi @rhuss

Thank you for your contribution 🥇

I think that is OK because matches with the scaffold of kubebuilder: https://github.com/kubernetes-sigs/kubebuilder/blob/master/testdata/project-v4/Makefile

However, you need to run make install and make generate locally to ensure that those files are properly updated in the testdata.