[TODO] Migrate to pydantic V2

[alextremblay]

involves porting our custom BaseSettings class to use pydantic-settings

also involves migrating all our BaseModel instances to the new V2 structure as per https://docs.pydantic.dev/2.0/migration/

[alextremblay]

this one's gonna be a doozy:

copier==8.1.0 [requires: pydantic>=1.10.2,<2]
diffsync==1.8.0 [requires: pydantic>=1.7.4,<2.0.0,!=1.8.1,!=1.8]
uoft-core==0.0.post395+g23ebab2.d20231204 [requires: pydantic>=1.9,<2.0]

all of these need to be updated to support pydantic V2

[alextremblay]

copier v9 depends on pydantic v2, so that's an easy fix.
uoft-core is gonna take a fair bit of work
the bigger issue is diffsync. diffsync still depends on pydantic v1. there's an unreleased diffsync v2 which depends on pydantic v2, but it's not out yet. we need to wait for this networktocode/diffsync#232 and then wait for nautobot-ssot==1.3.2 [requires: diffsync>=1.6.0,<2.0.0] to cut a new release depending on diffsync v2, and then we can upgrade to pydantic v2