[FEATURE] Allow for Gaia servers other than the default ESA

[geoffreymo]

Is your feature request related to a problem? Please describe.
The DRP can't run when the ESA Gaia server goes down, which it can for several days.

Describe the solution you'd like
The DRP runs, using another Gaia server such as ARI (https://gaia.ari.uni-heidelberg.de/index.html).

Describe alternatives you've considered
Waiting until the server comes back up, but then any time-sensitive observations (e.g., of fast-fading transients) would have to be hand-reduced.