Add mean/median method to the blockwise.apply() function

[marinebcht]

After #914

Proposition like coreg in coregister_3d:

blockwise = xdem.coreg.BlockwiseCoreg(xdem.coreg.NuthKaab(), block_size_fit=400, chunk_size_apply=100)
blockwise.fit(ref_dem, tba_dem)

ransac_apply_method = RansacApply(threshold_ransac=0.01, max_iterations_ransac=2000)

mean_apply_method = AffineApply(method="mean", min_samples=...) # min_samples absolut/relative ? 

aligned_dem_ransac = blockwise.apply()
blockwise.apply(fit_plan=ransac_apply_method)

def RansacApply():
    def __init__(threshold_ransac, max_iterations_ransac):
    def _apply(...) -> Raster # call map_overlap_multiproc_save() +  _wrapper_apply_epc()

def AffineApply(): # change name
    def __init__(method, min_samples):
    def _apply(...) -> Raster # call something like apply_matrix_multiproc_save() +  method()