S3 Storage Configuration documentation requires improvements

I tried to use the S3 Storage Configuration official documentation and my experience is that is doesn't allow to get a working S3 RSE. Among the issues experienced (thanks for the help on Mattermost!), I identified:

• lfn2pfn_algorithm must be defined at creation time (not sure how) as it cannot be changed once it is set (according to https://rucio.github.io/documentation/operator/configuration_parameters/#rse-settings) and in fact is refused by rucio rse update (or its rucio-admin equivalent).
• s3_url_style must be set to path, except if the RSE is in Amazon
• impl must set to rucio.rse.protocols.gfal.NoRename instead of the suggested rucio.rse.protocols.gfal.Default in the documentation mentioned above

Start with the linked S3 Storage Configuration page and the RSE settings documentation, then compare the listed options with the rucio rse update behavior described in the issue. Update the documentation to explain when lfn2pfn_algorithm must be set and to correct the s3_url_style and impl examples; done means the documented steps can produce a working S3 RSE.