feat: use INCUS_GLOBAL_CONF value

- set and pass INCUS_GLOBAL_CONF from makefile to terraform
- remove config_dir in all terragrunt.hcl files

Makefile

@@ -15,7 +15,6 @@ define vault_env
 	export TG_TF_PATH=terraform && \
 	eval "$$(vault read -format=json kv/data/service/terraform/incus \
 	  | jq -r '.data.data | to_entries[] | "export \(.key)=\(.value|@sh)"')" && \
-	export INCUS_INSECURE_TLS=1 && \
 	export INCUS_GLOBAL_CONF=$$(mktemp -d) && \
 	trap "rm -rf $$INCUS_GLOBAL_CONF" EXIT && \
 	mkdir -p $$INCUS_GLOBAL_CONF && \