python3-pyodbc needed in EL7

[SwooshyCueb]

This seemed to me to be the most appropriate location for this issue, though it could be argued that it belongs in the main irods repo instead.

EL7 (Centos 7, RHEL 7, and friends) needs a python3-pyodbc package. All other distros we support provide this already. See irods/irods#6322 for more information.

Given that this is only needed for one distro, this will likely be the first (or one of the first) repositories in our (not yet created) packaging namespace in github, rather than being added to our externals repository.