Update Dockerfile (add renku_save to RProfile.site + session hook)

1 job for master in 35 seconds (queued for 1 second)
Name Stage Failure
failed
image_build Build
Configure a credential helper to remove this warning. See
https://docs.docker.com/engine/reference/commandline/login/#credentials-store

Login Succeeded
$ CI_COMMIT_SHA_7=$(echo $CI_COMMIT_SHA | cut -c1-7) # collapsed multi-line command
Sending build context to Docker daemon 140.3kB
Error response from daemon: dockerfile parse error line 78: unknown instruction: RENKU_GET_DIR
Cleaning up file based variables
ERROR: Job failed: exit code 1