Leading slash in SOURCE_GITLAB_FILEPATH fails without warning

[sverrehu]

Using SOURCE_GITLAB_FILEPATH="/foo/bar.csv" with a leading slash, and a non-existing file, makes Kafka Security Manager log the following:

[2020-09-01 14:00:35,365] INFO No changes were detected in the ACL file /foo/bar.csv. Skipping ....  (com.github.simplesteph.ksm.source.GitLabSourceAcl)

even though there are no foo/bar.csv in the repository. I guess this is caused by GitLabSourceAcl.scala including $filepath verbatim in the GitLab API URL, thus requesting:

https://gitlab.com/api/v4/projects/.../repository/files//foo/bar.csv

GitLab will return a 308 redirect to a new URL leading to 404, but I guess this redirect is not followed, and that the <400 status is not flagged as en error.