refactor: convert enums to unions (#18900)

lib/modules/datasource/docker/index.spec.ts

lib/modules/datasource/docker/index.ts

lib/modules/datasource/docker/types.ts

lib/modules/manager/terraform/common.ts

lib/modules/manager/terraform/extract.ts

lib/modules/manager/terraform/extract/kubernetes.ts

lib/modules/manager/terraform/modules.ts

lib/modules/manager/terraform/providers.ts

lib/modules/manager/terraform/required-providers.ts

lib/modules/manager/terraform/required-version.ts

lib/modules/manager/terraform/resources.ts

lib/modules/manager/terraform/util.spec.ts

lib/modules/manager/terraform/util.ts

lib/modules/platform/azure/index.spec.ts

lib/modules/platform/azure/index.ts

lib/modules/platform/azure/types.ts

lib/modules/platform/bitbucket-server/index.spec.ts

lib/modules/platform/bitbucket-server/index.ts

lib/modules/platform/bitbucket/index.spec.ts

lib/modules/platform/bitbucket/index.ts