Decommissioning mira-fs0/fs1: alcf#dtn_theta Globus Endpoint Expanded

After preventative maintenance on May 3, alcf#dtn_theta will be expanded to include most of the former Mira data transfer nodes (DTNs). Note that after this change, alcf#dtn_theta will use the full pool of DTNs, so there will be no performance-related reasons to choose alcf#dtn_mira anymore and we strongly urge users to start using alcf#dtn_theta instead (to transfer data to/from theta-fs0). Any workflows referencing alcf#dtn_mira Globus endpoint should be updated to alcf#dtn_theta. The alcf#dtn_mira Globus endpoint will be removed on May 17.