Implement end-to-end test suite

[ben-z]

Implement a test suite that can be run in CI. A rough structure of the tests can be:

• Use moto or start a local S3-compatible storage system (e.g. minio).
• Create various test fixtures (local git repos that contain certain files on certain branches)
• Write tests for at least the following cases
  • moving files from temp to perm
  • moving files from perm to off-perm
  • moving files from off-perm to perm
  • files on different branches
  • repos without any watcloud URIs
• Run tests in CI