Use normal image tags

What does this MR do?

The current image names are overly verbose and unconventional. But more importantly, each release technically being the latest tag on a separate repository prevents us from using the docker datasource for auto-updating this image in downstream dependencies (auto-deploy-image and cluster-applications).

Testing

I also pushed this branch to a fork, see https://gitlab.com/hfyngvason/helm-install-image/container_registry

Relation to renovate

The idea is that we can then change auto-deploy-image's base image versioning to a single HELM_INSTALL_IMAGE_VERSION, and bump it with renovate using the following repository config:

{
   ...
    repositories: [
        {
            enabled: true,
            repository: "gitlab-org/cluster-integration/auto-deploy-image",
            semanticCommits: true,
            semanticCommitType: "feat",
            commitMessageExtra: "to {{{newValue}}}",
            enabledManagers: ["regex"],
            regexManagers: [
                {
                    enabled: true,
                    fileMatch: [".gitlab-ci.yml"],
                    matchStrings: [
                        "HELM_INSTALL_IMAGE_VERSION: (?<currentValue>.*)\n",
                    ],
                    depNameTemplate: "helm-install-image",
                    packageNameTemplate: "registry.gitlab.com/gitlab-org/cluster-integration/helm-install-image",
                    datasourceTemplate: "docker",
                },
            ],
        },
    ],
}

Example result from a local repo: