Replace xenon_secrets with utilix config file

Created by: ershockley

This should not be merged yet

This PR is a proposal to replace the xenon_secrets python file with the configuration file handled by utilix. This is helpful for running strax on e.g. OSG or anywhere else where a xenon_secrets.py file might not be present. I also prefer this type of text file configuration, which one could modify and/or have multiple copies of in case you want to change anything (e.g. I have a 1T config and an nT one, and just need to change XENON_CONFIG env variable to switch between the two).

In addition, it uses the utilix wrapper around pymongo, which increases readability and centralizes the runDB stuff.

I'm still testing some things, but wanted to get people's thoughts on something like this. If we don't want to go this route I need a different solution for OSG.

As an example, my utilix config file now looks like this (removing the actual content to be overly cautious)

[RunDB]
rundb_api_url =
rundb_api_user =
rundb_api_password = 
pymongo_url = 
pymongo_user = 
pymongo_password = 
pymongo_database = 

[straxen]
s3_access_key_id = 
s3_secret_access_key = 

In this way we can combine configuration of many things into a single file. For more info on utilix config, see here.

This should not be merged yet