allow setting s3 concurrency, proxy, timeout, uploadPartSize, putSizeLimit, version, and verify_bucket_exists

[jessebot]

Adds missing S3 related environment variables. Fixes #2270

Per the docs here's the missing supported S3 parameters:

• concurrency defaults to 5 [Note: This defines the maximum number of concurrent multipart uploads]

• proxy defaults to false

• timeout defaults to 15

• uploadPartSize defaults to 524288000

• putSizeLimit defaults to 104857600

• version defaults to latest

• useMultipartCopy defaults to true

• copySizeLimit defaults to 5242880000

• verify_bucket_exists defaults to true [Note: Setting this to false after confirming the bucket has been created may provide a performance benefit, but may not be possible in multibucket scenarios.]

This also helps us get ready to merge nextcloud/helm#614 downstream 🙏

Let me know if you need anything else :)