Add DFSET & PACKAGER ARGs to Exporter Dockerfile (#1827)
Add DFSET & PACKAGER ARGs to Exporter Dockerfile (#1827)

Adds the DFSET and PACKAGER ARG instructions to the
crunchy-postgres-exporter Dockerfile as needed to ensure the proper
detection of "rhel" or "centos" for the DFSET env var, and the use of
the proper package manager when installing the packages required by the
Crunchy PostgreSQL Exporter.
CrunchyData/postgres-operator,CrunchyData/postgres-operator