Add the possibility for user to specify the disaggregation bins

[mmpagani]

In the current disaggregation analysis, the user specifies the number of intervals or the bin width of the quantities used in a disaggregation. When the user wants to aggregate the results of different analyses, this option is unideal and it's more convenient to specify a priory the disaggregation matrix. A second use case is when the user prefers unevenly binning the disaggregation matrix.

Here are links to the code defining the bin edges:

• Magnitude https://github.com/gem/oq-engine/blob/master/openquake/hazardlib/calc/disagg.py#L381
• Distance https://github.com/gem/oq-engine/blob/master/openquake/hazardlib/calc/disagg.py#L401
• Other https://github.com/gem/oq-engine/blob/master/openquake/hazardlib/calc/disagg.py#L404

[mmpagani]

See https://github.com/gem/oq-engine/pull/8158