Adds non-periodic ("outflow") case for 2D Burgers'

[cwentland0]

Implements a 2D Burgers' case which features homogeneous Dirichlet BCs on the bottom and left boundaries, and homogeneous Neumann BCs on the top and right boundaries. This allows the Gaussian pulse IC to advect out of the domain, rather than following the previously-fixed periodic BCs. This case is largely just to simplify the Schwarz work, but also makes the 2D Burgers' case more generic. Also, this PR:

• Updates the problem constructors to follow the more generic "create_problem_eigen" format
• Adds the more generic problem parameterization that has been implemented for 2D Euler and 2D SWE
• Adds all necessary mechanisms for 2D Burgers Schwarz coupling
• Adds relevant tests for new case