Fix use of new configuration key
This MR fixes the ability to use the new GWDataFindServer
top-level configuration section name, which was broken:
...
File "/opt/gwdatafind-server/lib/python3.10/site-packages/gwdatafind_server/app.py", line 37, in __init__
config.get("GWDataFindServer", config["LDRDataFindServer"]),
File "/opt/gwdatafind-server/lib/python3.10/site-packages/configobj.py", line 554, in __getitem__
val = dict.__getitem__(self, key)
KeyError: 'LDRDataFindServer'