Updates needed for pydantic v2

[dougiesquire]

Description

Pydantic v2 was released on July 1. Intake-ESM uses pydantic, but does not work with pydantic v2. Simply importing Intake-ESM with pydantic=v2.0 results in an error.

A few syntactical updated throughout Intake-ESM should resolve this issue.

What I Did

# With pydantic=v2.0
import intake_esm

gives

~/miniconda3/envs/test/lib/python3.11/site-packages/pydantic/_internal/_config.py:257: UserWarning: Valid config keys have changed in V2:
* 'validate_all' has been renamed to 'validate_default'
  warnings.warn(message, UserWarning)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "~/miniconda3/envs/test/lib/python3.11/site-packages/intake_esm/__init__.py", line 9, in <module>
    from .core import esm_datastore
  File "~/miniconda3/envs/test/lib/python3.11/site-packages/intake_esm/core.py", line 21, in <module>
    from .cat import ESMCatalogModel
  File "~/miniconda3/envs/test/lib/python3.11/site-packages/intake_esm/cat.py", line 68, in <module>
    class Assets(pydantic.BaseModel):
  File "~/miniconda3/envs/test/lib/python3.11/site-packages/intake_esm/cat.py", line 77, in Assets
    @pydantic.root_validator
     ^^^^^^^^^^^^^^^^^^^^^^^
  File "~/miniconda3/envs/test/lib/python3.11/site-packages/pydantic/deprecated/class_validators.py", line 222, in root_validator
    return root_validator()(*__args)  # type: ignore
           ^^^^^^^^^^^^^^^^
  File "~/miniconda3/envs/test/lib/python3.11/site-packages/pydantic/deprecated/class_validators.py", line 228, in root_validator
    raise PydanticUserError(
pydantic.errors.PydanticUserError: If you use `@root_validator` with pre=False (the default) you MUST specify `skip_on_failure=True`. Note that `@root_validator` is deprecated and should be replaced with `@model_validator`.

For further information visit https://errors.pydantic.dev/2.0/u/root-validator-pre-skip