Add S3 (with Minio) netCDF open/read and processing and exploratory tests

[valeriupredoi]

First instance of a functional, end-to-end test of running PyActiveStorage on netCDF files on S3: I used Minio as S3-type storage with @sd109 having confirmed that that thing is identical to AWS S3 (cheers!). The workflow does this:

• Active now needs a new kwarg storage_type which could be None or could be s3 at the mo
• if it's s3 then it goes about and does the two file loads that are currently done in its bellows (ie open file, to get metadata/headers, NOT data) via a dedicated S3 mechanism that uses s3fs (note that fsspec does that too, fsspec calls s3fs when it recognized the FS to be S3, so no point using fsspec); then it goes about and uses h5netcdf to put the open file (which is nothing more than a memory view of the netCDF file) into an hdf5/netCDF-like object format
• chunks access and indexing is done as per normal via the s3_reduce_chunk() func that @markgoddard put in the previous PR, and from there on, Active works as per normal

Lazy transfer from s3fs

@bnlawrence has investigated the play between fsspec and s3fs via h5netcdf and found out thatwhen pulling the file from S3 via s3fs and convert-opening it with h5netcdf things get done lazily ie no actual data transfer, but only file's metadata headers. Cheers, Bryan!

[codecov]

Codecov Report

Patch coverage: 74.35% and project coverage change: -1.17 ⚠️

Comparison is base (5becf10) 87.21% compared to head (8bf1454) 86.04%.

❗ Current head 8bf1454 differs from pull request most recent head f401deb. Consider uploading reports for the commit f401deb to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #89      +/-   ##
==========================================
- Coverage   87.21%   86.04%   -1.17%     
==========================================
  Files           8        8              
  Lines         485      516      +31     
==========================================
+ Hits          423      444      +21     
- Misses         62       72      +10     

Impacted Files	Coverage Δ
activestorage/netcdf_to_zarr.py	85.71% <69.23%> (-6.60%)	⬇️
activestorage/active.py	92.13% <76.92%> (-2.77%)	⬇️

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[valeriupredoi]

gonna merge this since it's getting a bit too big for a regular PR and commit fluff keeps accruing - the only outstanding issue about it is the storage_type kwarg to Active that should/could be picked up from file name as @davidhassell suggested offline - but we can change that later (am not 100% sure we should, though, since future possible storage types may not necessarily be guessed from file name)