Consider `AsyncConnector` object for async interface

[jackwotherspoon]

Feature Description

Currently the Connector object is the main entrypoint for both synchronous and async driver implementations.

The synchronous drivers are called via connector.connect while the async drivers via connector.connect_async with the synchronous version basically just being a simple wrapper around the async method.

This issue is to keep an eye on considering moving the async drivers to a separate object and entrypoint of AsyncConnector.

This would allow for clear distinctions between the two and give flexibility in the interfaces moving forward.

Sample code

# current implementation
async def main():
    # get current running event loop to be used with Connector
    loop = asyncio.get_running_loop()
    # intialize Connector object as async context manager
    async with Connector(loop=loop) as connector:
        # create connection to Cloud SQL database
        conn: asyncpg.Connection = await connector.connect_async(
            "project:region:instance",  # Cloud SQL instance connection name
            "asyncpg",
            user="my-user",
            password="my-password",
            db="my-db-name"
            # ... additional database driver args
        )

# new AsyncConnector object
async def main():
    async with AsyncConnector() as connector:
        # create connection to Cloud SQL database
        conn: asyncpg.Connection = await connector.connect(
            "project:region:instance",  # Cloud SQL instance connection name
            "asyncpg",
            user="my-user",
            password="my-password",
            db="my-db-name"
            # ... additional database driver args
        )

Alternatives Considered

No response

Additional Details

No response