switch survey name to rubin_sim

[mschwamb]

switch survey name to rubin_sim so that it's clear this is running on rubin_sim simulated pointing databases. This way we can start to develop the version that will use the real rubin pointing data as "lsst"

Fixes #886 .

Describe your changes.

Review Checklist for Source Code Changes

• Does pip install still work?
• Have you written a unit test for any new functions?
• Do all the units tests run successfully?
• Does Sorcha run successfully on a test set of input files/databases?
• Have you used black on the files you have updated to confirm python programming style guide enforcement?

[astronomerritt]

Looks good. Thanks for making the change - looks like it was another one of those fiddly ones.