Improve docs on adding Google secrets in AWS Secrets Manager (apache#…

…42832)

The [existing documentation](https://airflow.apache.org/docs/apache-airflow-providers-amazon/stable/secrets-backends/aws-secrets-manager.html#example-of-storing-google-secrets-in-aws-secrets-manager) on how to set up Google secrets in AWS Secrets Manager is out of date. It led me on a merry chase for hours.

I hereby submit this PR to update the doc. I solemnly swear that the content has been verified using DAG code similar to this

```python
gsheet = GSheetsHook(gcp_conn_id=gcp_conn_id)
values = gsheet.get_values(
    spreadsheet_id=spreadsheet_id,
    range_=f"{sheet_name}!B1:B2",
)
`

docs/apache-airflow-providers-amazon/secrets-backends/aws-secrets-manager.rst

@@ -161,10 +161,22 @@ For example, if you want to only lookup connections starting by "m" in AWS Secre
 
 Example of storing Google Secrets in AWS Secrets Manager
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-For connecting to a google cloud conn, all the fields must be in the extra field, and their names follow the pattern
-``extra_google_cloud_platform__value``. For example:
+For connecting to a google cloud connection, all the fields must be in the extra field. For example:
+
+If you are using the key file:
 
 .. code-block:: ini
 
-  {'key_path': '/opt/airflow/service_account.json',
-  'scope': 'https://www.googleapis.com/auth/devstorage.read_only'}
+  {"extra": {"key_path": "/opt/airflow/service_account.json",
+  "scope": "https://www.googleapis.com/auth/devstorage.read_only"}}
+
+If you are using the key dictionary.
+
+.. code-block:: ini
+
+  {"extra": {"keyfile_dict": "<copy & paste the service account json here>",
+  "scope": "https://www.googleapis.com/auth/devstorage.read_only"}}
+
+Either way you can edit the ``Key/value`` pairs directly on the UI
+
+.. image:: /img/aws-secrets-manager-gcp.png