S3 client: add IAM configuration

[yankovs]

This PR adds the ability to support IAM authentication using a iam_auth boolean option in the [s3] section of karton.ini, much like in MWDB.

Testing was done on karton-core v5.2 and mwdb-core v2.8.2, by omitting the access_key and secret_key from karton.ini and making sure everything is functional:

• File upload to mwdb
• File reanalysis
• Making new kartons

This PR is marked as draft because the configuration wizard of Karton seems like an ancient piece of code and I'm not sure if I should add this option to it or not

[psrok1]

@yankovs I think you don't need to bother of this karton.main. It's just a very simple utility and no need to cover all configuration options.

I'm also pre-approving your changes, code looks good!

When you feel ready with the PR, rebase your branch as I fixed some CI issues in the meantime.

[yankovs]

Mhm, seems like mypy doesn't like botocore since it doesn't have typings 🤔.
I've tried adding botocore-stubs to project requirements and it seems to solve the issue, but I'm not sure if this a good solution since you could also probably disable mypy altogether (like in mwdb-core) or manually disable errors for botocore.

[psrok1]

botocore-stubs looks ok. Actually I'm amazed that someone managed to make such quality typings for botocore 😄 We don't really want to disable mypy as it helped many times to avoid errors.