feat: enable incus support in actionsdind container (#10)

- add incus-images backend
- set incus-images as default backend

Reviewed-on: https://git.query.consul/unkin/packer-images/pulls/10

Makefile

@@ -91,6 +91,8 @@ $(DIRS):
 	export SUFFIX=$(SUFFIX) && \
 	export GIT_COMMIT=$(GIT_COMMIT) && \
 	export GIT_BRANCH=$(GIT_BRANCH) && \
+	export VAULT_ADDR=https://vault.query.consul:8200
+	export VAULT_TOKEN=$$(vault write -field=token auth/approle/login role_id=$$VAULT_ROLEID) && \
 	/usr/bin/packer init . && \
 	/usr/bin/packer build . )