add e2e specs for oras attach

[qweeah]

Happy paths:

• should attach files to a subject in a remote registry
• should attach files with customized media types to a remote registry
• should attach with customized media type when building the manifest
• should attach via referrer tag schema and referrer API
• should attach using image manifest and customized config
• should attach and export the built manifest

Bad paths:

• should fail directly if not logged in
• should fail if no subject reference provided
• should fail if no file reference or manifest annotation provided