Update deprecated map_metric import in custom

[cdkini]

Hey there! I'm a core dev on the GX team and am currently working through cleaning up some deprecated code as part of our v16 release.

One of these items happens to be the great_expectations.expectations.metrics.map_metric import - this has been renamed to great_expectations.expectations.metrics.map_metric_provider as of v0.13 and per our policy of removing deprecated code after two minor versions, I'm hoping to delete as much old code as possible.

I've proposed the necessary change below. Thanks!

[denimalpaca]

@cdkini Is this a breaking change? Want to know if the next release will have to have a major version bump. Or is it just going to rely on GX >= 16?

In the latter case, https://github.com/astronomer/airflow-provider-great-expectations/blob/main/setup.cfg#L37 should be updated as well.

[denimalpaca]

@cdkini could you please comment on the above? Would love to merge this today

[cdkini]

@denimalpaca apologies for the delay! No additional changes are necessary - great_expectations.expectations.metrics.map_metric_provider has been around since v13 so the current GX pin should be sufficient