s3:// wrapper can't be used for image fields

Problem/Motivation

Steps to reproduce:

• Create an image field using s3 stream wrapper.
• Upload a file.
• Attempt to save node results in fatal.
• getimagesize call inside image_get_info tries to do a seek on the remote stream
• seeking on a remote stream isn't supported for memory reasons
• getimagesize returns false
• attempt to write image width/height values into field tables results in an sql error

Proposed resolution

Borrow from s3fs project and wrap the guzzle body object in a cached stream - which does support seeking, by reading the remote file into temporary memory
This only impacts content editors so memory impact isn't large unless you're allowing open content-creation.

Remaining tasks

Review

User interface changes

None

API changes

None

Data model changes