[AIRFLOW-5906] Add authenticator parameter to snowflake_hook

[koszti]

To use Snowflake with SSO, Okta, ADFS or any other SAML 2.0 compliant identify provider we need to pass the authenticator=externalbrowser extra parameter to the snowflake connection string. Currently the authenticator parameter not extracted from the connection extras JSON and not possible to use Airflow and Snowflake with SAML/SSO

This PR extracts the authenticator parameter from the connection "extra"s JSON and passing it to the snowflake uri. This allows to use Airflow and Snowflake configured with SAML/SSO.

Example airflow connection config:

Conn Id: <CONNECTION_ID>
Conn Type: Snowflake
Host: <YOUR_SNOWFLAKE_HOSTNAME>
Schema: <YOUR_SNOWFLAKE_SCHEMA>
Login: <YOUR_SNOWFLAKE_USERNAME>
Password: <YOUR_SNOWFLAKE_PASSWORD>
Extra: {
        "account": <YOUR_SNOWFLAKE_ACCOUNT_NAME>,
        "warehouse": <YOUR_SNOWFLAKE_WAREHOUSE_NAME>,
         "database": <YOUR_SNOWFLAKE_DB_NAME>,
         "region": <YOUR_SNOWFLAKE_HOSTED_REGION>,
         "authenticator": "externalbrowser"
    }

Related snowflake documentation with the valid authentication strings: Snowflake Python: Connecting using Federated Authentication

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[boring-cyborg]

Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contribution Guide (https://github.com/apache/airflow/blob/master/CONTRIBUTING.rst)
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[kaxil]

This test is not related to the changes in this PR. It just checks if extra_dejson of any Connection object is changed, they are reflected and can be retrieved with get_uri().

[boring-cyborg]

Awesome work, congrats on your first merged pull request!