Make host/port configurable for Snowflake connections

[whummer]

First of all - thanks so much for building Airflow, it is an absolutely awesome platform! 🙌 🚀

This PR extends the functionality of SnowflakeHook to make the host/port configurable for Snowflake connections. This facilitates testing against non-standard Snowflake endpoints, for example when testing against LocalStack (a local cloud emulator).

A similar PR has been created against the Astronomer Cosmos repo some time ago (see astronomer/astronomer-cosmos#1063), and our users have now requested to use the standard Airflow Snowflake connector with LocalStack Snowflake as well.

The PR also updates the documentation for the Snowflake connector, but it does not contain any tests at this point. If adding a test is required, then any pointers or guidance would be appreciated. 👍

Testing

Tested this locally against the LocalStack Snowflake emulator - with a connection config like this:

... and a simple DAG like this:

from airflow import DAG
from airflow.providers.snowflake.operators.snowflake import SnowflakeOperator

conn_id = "snowflake_local"

dag = DAG(
    'snowflake_test',
    default_args={'snowflake_conn_id': conn_id},
    tags=['example'],
    catchup=False,
)

snowflake_op_sql_str = SnowflakeOperator(
    task_id='query1',
    dag=dag,
    sql="SELECT CURRENT_ACCOUNT()",
)

... the DAG executes successfully, and outputs:

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[potiuk]

For that kind of change tests are not needed (other than testing when we release it)