Add support for custom key:value tags for files generated by Nextflow and stored in Azure and GCP cloud storage

[robnewman]

Improvement

Currently, the Nextflow publishDir directive allows users to publish workflow files into a specific folder in cloud storage and (for Amazon S3 only as of writing) associate custom key:value tags with the published files.

As Nextflow is used across all the major cloud providers, it would be appropriate to support custom key:value tags in both Microsoft Azure and Google Cloud platforms.

Usage scenario

Resources generated by Nextflow pipelines can optionally have custom tags associated with them, and have that functionality consistent across the major cloud providers (not just Amazon S3 cloud storage).

[stale]

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