Configure the config server via an environment variable

[rtuck99]

Required in order to fix the mx-bluesky system tests, since the config server needs to be configurable in order to point against the system test daq-config-server.

See also mx-bluesky PR

• Support configuring the config server URL mx-bluesky#1698

Instructions to reviewer on how to test:

1. Do thing x
2. Confirm thing y happens

Checks for reviewer

• Would the PR title make sense to a scientist on a set of release notes
• If a new device has been added does it follow the standards
• If changing the API for a pre-existing device, ensure that any beamlines using this device have updated their Bluesky plans accordingly
• Have the connection tests for the relevant beamline(s) been run via dodal connect ${BEAMLINE}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.08%. Comparing base (8cf8dfb) to head (24812af).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2008   +/-   ##
=======================================
  Coverage   99.08%   99.08%           
=======================================
  Files         319      319           
  Lines       12412    12414    +2     
=======================================
+ Hits        12299    12301    +2     
  Misses        113      113           

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