[ITensorMPS] DMRG eigsolve keyword argument names

Right now, the convention for setting eigsolve keyword arguments through DMRG is the following:

dmrg(H, psi0, sweeps;
     eigsolve_tol = 1e-14,
     eigsolve_krylovdim = 3,
     eigsolve_maxiter = 1,
     eigsolve_verbosity = 0)

Instead, we could pack them all into a single keyword argument eigsolve, and pass them as a NamedTuple:

dmrg(H, psi0, sweeps; eigsolve = (tol = 1e-14, krylovdim = 3, maxiter = 1, verbosity = 0))

This could be a commonly used code pattern for keyword arguments that are passed through a high level function to some lower level function (for example, it could be used in factorize for passing keyword arguments to svd about what kind of SVD algorithm to use).