Why does the argument order of `pyconvert_add_rule` deviate from convention

According to the [Julia Docs](https://docs.julialang.org/en/v1/manual/style-guide/#Write-functions-with-argument-ordering-similar-to-Julia-Base), function arguments should be placed first because "Putting a function argument first permits the use of [do](https://docs.julialang.org/en/v1/base/base/#do) blocks for passing multiline anonymous functions."

Is there a reason for not following this convention?
Would it be reasonable to support the conventional argument order in addition to the current argument order?
Can we switch fully to the conventional argument order and deprecate the current argument order / remove it in the next breaking release?

Start by locating the pyconvert_add_rule definition and its current callers. Review the Julia argument-ordering convention and determine which argument order should be supported, including the compatibility and deprecation decision; done means the API direction is agreed and documented.

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