Add coalesce option to join_asof

[deanm0000]

Problem description

Let's say you have

df1 = pl.DataFrame({
    "a": [1, 2, 4, 5, 6, 7]
}).sort('a')

df2 = pl.DataFrame({
    "a": [1, 3, 5, 7],
    "b": [1, 3, 5, 7]
}).sort('a')

and you want to do a join_asof by column a but you want to keep both as for filtering purposes

Right now, if I'm not mistaken, I think you'd have to do:

df1.join_asof(df2.with_columns(pl.col('a').alias('a_right')), on = "a")

it'd be nice if we could do df1.join_asof(df2, on = "a", keep_right=True)

[knl]

This would be quite useful! I came to submit virtually the same issue :)