We can be better at checking `buffer_size` and `chunk_size` for S3 repositories.
For example, we know that:
* `buffer_size` should be more than `5mb`
* `chunk_size` should be no more than `5tb`
* `buffer_size` should be lower than `chunk_size`
Otherwise, setting `buffer_size` is useless.
For the record:
`chunk_size` is a Snapshot setting whatever the implementation is.
`buffer_size` is an S3 implementation setting.
Let say that you are snapshotting a 500mb file. If you set `chunk_size` to `200mb`, then Snapshot service will call S3 repository to snapshot 3 files with the following sizes:
* `200mb`
* `200mb`
* `100mb`
If you set `buffer_size` to `100mb` (AWS maximum size recommendation), the first file of `200mb` will be uploaded on S3 using the multipart feature in 2 chunks and the workflow is basically the following:
* create the multipart request and get back an `id` from AWS S3 platform
* upload part1: `100mb`
* upload part2: `100mb`
* "commit" the full upload using the `id`.
Closes#17244.
e907b7c11e