packaging: oci: provide INSTALL_DIR

This value is needed to package the content of the install dir as the
root of the package. Not providing it will cause the package to contain
the full path (/opt/datadog-packages/datadog-agent/foo instead of /foo)

.gitlab/packaging/oci.yml

@@ -63,6 +63,8 @@ packaging_oci:
     - $S3_CP_CMD merged.tar $S3_ARTIFACTS_URI/datadog-agent_7_oci.tar
   before_script:
     - source /root/.bashrc
+    - export PACKAGE_VERSION=$(inv agent.version --url-safe --major-version 7)-1
+    - export INSTALL_DIR=/opt/datadog-packages/${OCI_PRODUCT}/${PACKAGE_VERSION}
   artifacts:
     paths:
       - ${OMNIBUS_PACKAGE_DIR}