Add mod_s3_upload

[RomanHargrave]

Implements XEP-0363 using cloud storage. Great for clusters or people that don't have the bandwidth wherever the ejabbered service lives.

Provides the functionality requested in #305

[badlop]

Don't worry about the check fails, it's a problem in my github actions workflow. It should get fixed with this recent commit https://github.com/processone/ejabberd-contrib/commit/d536707e4f34797cd2ceb2767f438dfdf155866b

[Neustradamus]

@RomanHargrave: Good job, thanks!

Linked to:

• https://github.com/processone/ejabberd-contrib/issues/305
• https://github.com/processone/ejabberd/pull/3893
• https://github.com/processone/ejabberd/issues/3625
• https://github.com/processone/ejabberd/issues/3624