Azure batch currently uses a CentOS image which is EOL July 2024. We should change it to a supported image before then. Nextflow has started using Ubuntu:20.04 as the default image and seems to be going OK so we could copy this.

Nextflow PR: https://github.com/nextflow-io/nextflow/pull/2868

Azure Batch issue: https://github.com/Azure/Batch/issues/119