Enable CLI to bypass required flag "--beamline" if specified in env

[Kezzsim]

Resolves #189 by adding additional parsing logic to the CLI component which will get the beamline from the environment variable BEAMLINE_ACRONYM.

Some design consciderations:

• This is implemented in the CLI args parser section as to allow the user to still override the env var with an argument if needed, this seems like it would be more intuitive.
• Because of this decision, when invoking the function from within another python program; beamline will still need to be provided. This shouldn't be a huge deal because python scripting is automated and will be run by the machine and not a human. This entire endeavor is an ergonomic concern.

[tacaswell]

Is this still a going concern?