correct role handling and S3FS bypass

[ErinWeisbart]

Correct credential handling to enable AWS IAM role usage.

[ErinWeisbart]

Closes #132 by changing load_data_csv access to download.
Closes #114.

[ErinWeisbart]

Noting that S3FS bypass appears to be working fine and I had several tests of all the files downloading correctly and then apparently stochastically one run threw:
OSError: [Errno 30] Read-only file system: '/home/ubuntu/local_input/path/to/image/cdp2bioactives_a22_s4_w33236d730-2143-4738-bfac-685f917a717d.tif.2FE98647'

[ErinWeisbart]

Full S3FS bypass is working at this point.
Still haven't finished necessary changes to run-worker.sh to make it mount S3 bucket using new credential handling.

[ErinWeisbart]

I have this branch running on a dataset now and it works (!), successfully completely bypassing S3FS and using a role.
(I don't know if it mounts S3 using a role, but I think it will be helpful to consider this a complete unit and troubleshoot S3 mounting with a role if necessary in a separate PR).

[bethac07]

Overall, this seems great, and super exciting that it's working! Thank you so much

For future, tiiiiiny nitpick - would be great to not mix in a ton of stylistic changes (like "->' in a PR like this already making big behavior changes, or at least make those an explicit commit, just to a) keep the size and readability of the PR reasonable and b) assuming commits aren't squashed, by having them be an explicit commit, you see that that's why a line was changed ("oh, that was done for stylistic reasons" as opposed to "wait, what does this have to do with role handling?"). For this one, there are a lot of commits, so up to you if you'd like us to squash or not, but just something small for the future.

Congrats on this, it was a huge achievement!

[ErinWeisbart]

Thanks @bethac07 !
Sorry, this PR kinda turned into a chaos of commits in all the troubleshooting. I'm not honestly sure how a lot of stylistic changes ended up being mixed in, but I will certainly try harder to keep them to their own commit in the future.