How to handle `monotonically_increasing/decreasing` attributes on non-unary OPs

Description

Recently we added monotonically_increasing and monotonically_decreasing attributes to UnaryScalarOP and this brought about a discussion around non-unary scalar operations that may be monotonic like Add/Max.

The two options that I can think off are:

1). move the attributes up onto ScalarOP and keep default as FALSE

2). Define special cases of non-unary scalar ops to have the attributes

I think that option one has the advantage that all ScalarOPS would be consistent with these attributes and would avoid a potential attribute error when something like op.scalar_op.monotonic_increasing is called on a Mul op. The disadvantage being how we define and use monotonicity, will it be monotonic in every input while holding the others fixed?

Option two I think would simpler, but would still require a definition of monotonicity for a non-unary operation.

Resolution to this topic would facilitate the completion of https://github.com/pymc-devs/pymc/issues/8259