Fix(snowflake): private_key should be bytes, update docs

docs/integrations/engines/snowflake.md

@@ -41,19 +41,42 @@ gateways:
 
 ### Snowflake Private Key Authorization
 
-SQLMesh supports Snowflake private key authorization connections by providing the path to the private key file. `account` and `user` are required. For example:
+SQLMesh supports Snowflake private key authorization connections by providing the private key bytes. Only config.py is supported when using private key authorization. `account` and `user` are required. For example:
+
+```python
+from sqlmesh.core.config import (
+    Config,
+    GatewayConfig,
+    ModelDefaultsConfig,
+    SnowflakeConnectionConfig,
+)
 
-```yaml
-gateways:
-    snowflake:
-        connection:
-            type: snowflake
-            account: ************
-            user: ************
-            private_key: /path/to/private/key
-            warehouse: ************
-            database: ************
-            role: ************
+from cryptography.hazmat.primitives import serialization
+
+key = """-----BEGIN PRIVATE KEY-----
+...
+-----END PRIVATE KEY-----""".encode()
+
+p_key= serialization.load_pem_private_key(key, password=None)
+
+pkb = p_key.private_bytes(
+    encoding=serialization.Encoding.DER,
+    format=serialization.PrivateFormat.PKCS8,
+    encryption_algorithm=serialization.NoEncryption(),
+)
+
+config = Config(
+    model_defaults=ModelDefaultsConfig(dialect="snowflake"),
+    gateways={
+       "my_gateway": GatewayConfig(
+            connection=SnowflakeConnectionConfig(
+                user="user",
+                account="account",
+                private_key=pkb,
+            ),
+        ),
+    }
+)
 ```
 
 The authenticator method is assumed to be `snowflake_jwt` when `private_key` is provided, but it can also be explicitly provided in the connection configuration.
@@ -79,4 +102,4 @@ sqlmesh_airflow = SQLMeshAirflow(
         "snowflake_conn_id": "<Connection ID>"
     },
 )
-```
+```

sqlmesh/core/config/connection.py

@@ -115,7 +115,7 @@ class SnowflakeConnectionConfig(ConnectionConfig):
         concurrent_tasks: The maximum number of tasks that can use this connection concurrently.
         authenticator: The optional authenticator name. Defaults to username/password authentication ("snowflake").
                        Options: https://github.com/snowflakedb/snowflake-connector-python/blob/e937591356c067a77f34a0a42328907fda792c23/src/snowflake/connector/network.py#L178-L183
-        private_key: The optional private key to use for authentication.
+        private_key: The optional private key to use for authentication. This is in the form of bytes and can only be created with the Python config. https://docs.snowflake.com/en/developer-guide/python-connector/python-connector-example#label-python-key-pair-authn-rotation
     """
 
     account: str
@@ -125,7 +125,7 @@ class SnowflakeConnectionConfig(ConnectionConfig):
     database: t.Optional[str] = None
     role: t.Optional[str] = None
     authenticator: t.Optional[str] = None
-    private_key: t.Optional[str] = None
+    private_key: t.Optional[bytes] = None
 
     concurrent_tasks: int = 4