Conditional imports to support operating with pydantic>2 installed

[chrisguidry]

Following the compatibility work we've done in prefect, we also want to apply the
same compatibility changes to all Prefect-maintained collections. We're following the
convention that Prefect will always use pydantic<2 idioms, leaning on the
pydantic.v1 module of pydantic>2 to aid us in this. With these changes, we can
operate normally regardless of the installed version.

Until prefect fully deprecates pydantic versions below 2.0, we'll continue to
maintain that constraint of using only v1 idioms.

This is part of a series of identical PRs for all of our maintained collections.