pkg/machine/ocipull: add custom policy.json location

The default policy file /etc/containers/policy.json location does not
work on windows and for packages that ship a default.

Now we search for the policy.json in the following overwrite locations:
macos and linux:
 - ~/.config/containers/policy.json
 - /etc/containers/policy.json
windows:
 - %APPDATA%\containers\policy.json

Also it offers an additional DefaultPolicyJSONPath var that should be
overwritten at built time with the path of the file that is shipped by
packagers. Thile file is used when none of the overwrite paths exist.

[NO NEW TESTS NEEDED]

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

pkg/machine/ocipull/policy_unix.go

@@ -0,0 +1,19 @@
+//go:build !windows
+
+package ocipull
+
+import (
+	"path/filepath"
+
+	"github.com/containers/common/pkg/config"
+	"github.com/containers/storage/pkg/homedir"
+)
+
+func localPolicyOverwrites() []string {
+	var dirs []string
+	if p, err := homedir.GetConfigHome(); err == nil {
+		dirs = append(dirs, filepath.Join(p, "containers", policyfile))
+	}
+	dirs = append(dirs, config.DefaultSignaturePolicyPath)
+	return dirs
+}