Bring Go client to functional parity of cli

Proposal

As per documentation pages the method to stream a specific file from allocation has multiple options, such as path, follow, offset and origin. Same options are available via both REST API and nomad operator api .... However Go client Client.AllocFs().Stream() accepts all of those except follow, it currently uses follow=true which there is no way to override.

Use-cases

• Retrieving single file that is not being written to
• Retrieving "point-in-time" of single file that is being actively written

Attempted Solutions

• Looked at using .Raw() but it requires way more coding around than I would like to.
• There is a .Cat() method, that does actually work as follow=false, but this is different from the Logs functionality where the same method is used for both using boolean argument as a switch.

Start in api/fs.go around the AllocFs().Stream() method and compare its arguments with the stream-file API documentation and the equivalent nomad operator api behavior. Confirm how follow is represented in the Go client, then verify that callers can retrieve both a complete file and a point-in-time snapshot without using Raw().