feat(makefile): set default melange runner to docker (#32207)

Continuous integration and automation runs pipelines in Docker with
Melange, in order to provide consistency and homogeneous environment, it
sets the default runner to Docker. The Make variable can be inherited
and overridden.

  Related:
  - chainguard-dev/melange#1611

Signed-off-by: Massimiliano Giovagnoli <[email protected]>

Makefile

@@ -11,6 +11,9 @@ KEY ?= local-melange.rsa
 REPO ?= $(shell pwd)/packages
 CACHE_DIR ?= gs://wolfi-sources/
 
+# Default Melange runner is Docker.
+MELANGE_RUNNER ?= docker
+
 MELANGE_OPTS += --repository-append ${REPO}
 MELANGE_OPTS += --keyring-append ${KEY}.pub
 MELANGE_OPTS += --signing-key ${KEY}
@@ -21,6 +24,7 @@ MELANGE_OPTS += --license 'Apache-2.0'
 MELANGE_OPTS += --git-repo-url 'https://github.com/wolfi-dev/os'
 MELANGE_OPTS += --generate-index false # TODO: This false gets parsed as argv not flag value!!!
 MELANGE_OPTS += --pipeline-dir ./pipelines/
+MELANGE_OPTS += --runner=$(MELANGE_RUNNER)
 MELANGE_OPTS += ${MELANGE_EXTRA_OPTS}
 
 # Enter interactive mode on failure for debug
@@ -41,6 +45,7 @@ MELANGE_TEST_OPTS += --repository-append https://packages.wolfi.dev/os
 MELANGE_TEST_OPTS += --keyring-append https://packages.wolfi.dev/os/wolfi-signing.rsa.pub
 MELANGE_TEST_OPTS += --test-package-append wolfi-base
 MELANGE_TEST_OPTS += --debug
+MELANGE_TEST_OPTS += --runner=$(MELANGE_RUNNER)
 MELANGE_TEST_OPTS += ${MELANGE_EXTRA_OPTS}
 
 ifeq (${USE_CACHE}, yes)