New Issue: allow changing job name prefix via CHPL_LAUNCHER_NAME_PREFIX

19600, "jhh67", "allow changing job name prefix via CHPL_LAUNCHER_NAME_PREFIX", "2022-04-05T18:41:25Z"

Chapel launchers currently prefix the job name with Chpl- or CHPL-. This makes it difficult to distinguish jobs on systems in which everyone shares the same user name. We should allow the job prefix to be changed via a CHPL_LAUNCHER_NAME_PREFIX environment variable.