fix: Fail early if private_key_path doesn't exist (#326)

This pull request includes an important update to the `get_private_key`
method in the `target_snowflake/connector.py` file. The changes enhance
logging and error handling when reading the private key from a file.

Enhancements to logging and error handling:

* Added a debug log statement to indicate when the private key is being
read from a file.
* Introduced a check to verify if the private key file exists before
attempting to read it, raising a `FileNotFoundError` with a descriptive
error message if the file is not found.

Author: kronnk

target_snowflake/connector.py

@@ -120,8 +120,13 @@ def get_private_key(self):
         phrase = self.config.get("private_key_passphrase")
         encoded_passphrase = phrase.encode() if phrase else None
         if "private_key_path" in self.config:
-            with Path(self.config["private_key_path"]).open("rb") as key:
-                key_content = key.read()
+            self.logger.debug("Reading private key from file: %s", self.config["private_key_path"])
+            key_path = Path(self.config["private_key_path"])
+            if not key_path.is_file():
+                error_message = f"Private key file not found: {key_path}"
+                raise FileNotFoundError(error_message)
+            with key_path.open("rb") as key_file:
+                key_content = key_file.read()
         else:
             key_content = self.config["private_key"].encode()