CLI help cache lookup fails when conda environment goes to read-only.

[ebolyen]

See this forum post for a better writeup than what follows below:
https://forum.qiime2.org/t/qiime-info-filenotfounderror-on-2024-10-amplicon-docker/32011/16

The issue is that q2cli.util.get_app_dir will start looking elsewhere for the cache because while the docker image writes the cache correctly to the conda env, it is later determined to be un-writable when converted to signularity and starts moving to other possible cache locations.

Perhaps we should check if the directory exists as expected before moving onward to the next options?
Or, we could always write the config/cache to the home directory which is the fallback when the system is read-only.