refactor: dataframe join params

[ion-elgreco]

Which issue does this PR close?

• related RFC: Re-work some DataFrame APIs #875

Rationale for this change

Many times join keys are the same in both dataframes, so a simple on suffices. Also join_keys are deprecated over left_on and right_on.

What changes are included in this PR?

• marks join_keys as deprecated
• introduces on, left_on, right_on parameters
• adds function overloads

Are there any user-facing changes?

• new params added, join_keys deprecated.

[timsaucer]

This looks like a good improvement.

[ion-elgreco]

This looks like a good improvement.

Any other changes still needed?

[timsaucer]

None that I can see. I'll run the workflow and as long as it all passes, I'll merge it later today

[timsaucer]

Thank you!

[timsaucer]

It looks like we do have some problems in pytests

[ion-elgreco]

@timsaucer Ah my bad, we need to add this at the end of the function, then it should run:

if isinstance(left_on,str):
    left_on=[left_on]
if isinstance(right_on,str):
    right_on=[right_on]

Can't add it now myself to test :(