ci: make "create cache" a reusable workflow

[romanc]

Description

Recent (planned) downtime of NCCS portal showed a whole in our translate test data caching strategy. When we run pyFV3 tests as re-usable workflow in e.g. NDSL tests, we don't cache the translate test data. To do so, we can "upgrade" the "create cache" workflow to be re-usable such that we can call it from e.g. NDSL when we create the cache there.

GHA doesn't provide a way to detect workflow_call as an event (e.g. github.event will be workflow_dispatch in that case, which is the same as for a manual dispatch). We thus create an artificial input in case the workflow is called from another workflow. That way we know. The artificial input has a default value such that we don't need to set it from the calling workflow.

How Has This Been Tested?

Tested on my fork, e.g. romanc/NDSL#5.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation: N/A
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
  Depends on ci: make "create cache" a reusable workflow pySHiELD#69
• New check tests, if applicable, are included: N/A
• Targeted model if this changed was triggered by a model need/shortcoming: N/A

[twicki]

Nice. I don't fully get the magic, but if it works it works!

[jjuyeonkim]

My experience with workflows is limited, so I don't have feedback other than it looks useful.