Allow transforms to produce main input, output

[sfc-gh-chu]

Items to add to release announcement:

• Heading: delete this list if this PR does not introduce any changes that need announcing.
• Optional args_transform and ret_transform arguments to Instrument.tracked_method_wrapper that will be called on arguments and return values to determine main input string and output string respectively

Other details that are good to know but need not be announced:

• There should be something here at least.
• No decided interface for this method yet. Can be a decorator argument

[sfc-gh-jreini]

Please add a usage example for this

[sfc-gh-jreini]

Please add a usage example for this

or rather, is this change a user-facing change? how can folks take advantage of this

[sfc-gh-chu]

@joshreini1 haven't had a chance to update here. This is an internal arg change for now. Will need to discuss with @piotrm0 how this looks in practice.