Add AppStream image with access to the XNAT VPC

[milanmlft]

• [x] Create Terraform module to deploy AppStream: HealthBioScienceIDEAS/terraform-aws-IDEAS-appstream#1
• [x] Make deploying the AppStream instance optional

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I think Appstream was being discussed as a potential for when we want people on the cloud to access image visualisation software. In this approach, they would neither have to install the software on their machine nor download any of the imaging data off the cloud onto their machine. Instead, they would log into a VM that has the software installed and can see the XNAT server created by Paul for the lesson and open it up to review to make sure the processing worked.

Appstream images can be made public, so what would have to be done is to modify one of the images that we have previously generated that has the software already on it and figure out what instuctions would be needed to make sure people could start that VM on the same VPC as the XNAT server so that they can access data from it.

Originally posted by @davecash75 in https://github.com/HealthBioscienceIDEAS/IDEAS/issues/19#issuecomment-1686628581

Goal of the AppStream image:

• Run software like FreeView or fsleyes to visualise the results from analyses run on XNAT
• Provide access to the XNAT VPC, so users have access to the data without having to download them lcoally

[milanmlft]

figure out what instructions would be needed to make sure people could start that VM on the same VPC as the XNAT server so that they can access data from it

as well as launching appstream in the same VPC as XNAT, you'll need to allow ingress to the EFS volume from appstream and mount the volume somewhere

Originally posted by @p-j-smith in https://github.com/HealthBioscienceIDEAS/IDEAS/issues/19#issuecomment-1687612569