Cortex-jsonnet 1.3.0

👋 This is the first release of cortex-jsonnet and it is compatible with Cortex 1.3.0.

Starting from now, we plan to:

• Release a new version of cortex-jsonnet for each Cortex stable minor version
• Match the cortex-jsonnet version number with the respective supported Cortex version
• Provide a changelog for significant changes