Add get_current_user function to oauth_util.py

[sanders41]

Is your feature request related to a specific problem?

oauth_util.py should have a get_current_user function

A description of what the problem is.
Ex. I'm always frustrated when [...]

Describe the solution you'd like

from fastapi import Depends, Security
from fastapi.security import SecurityScopes
from sqlalchemy.orm import Session

from fideslib.oauth.api.deps import get_db
from fideslib.models.fides_user import FidesUser

async def get_current_user(
    security_scopes: SecurityScopes,
    authorization: str = Security(oauth2_scheme),
    db: Session = Depends(get_db),
) -> FidesUser:
    """A wrapper around verify_oauth_client that returns that client's user if one exsits."""
    client = await verify_oauth_client(
        security_scopes=security_scopes,
        authorization=authorization,
        db=db,
    )
    return client.user

Describe alternatives you've considered, if any

Let each library implement their own version.

Additional context

Add any other context or screenshots about the feature request here.