Don't import dbutils.widget until use (#859)

## Changes
We should not call dbutils.widget in the init script. This causes
dbutils to internally try to import the widget implementation. When in
notebook environment, the widget implementation shows a special warning
which prompts users to install the sdk version with ipywidget support.

<img width="1059" alt="Screenshot 2023-09-05 at 19 28 24"
src="https://github.com/databricks/databricks-vscode/assets/88345179/59c65c39-5808-4601-8fa9-d17858520835">

## Tests
<!-- How is this tested? -->

packages/databricks-vscode/resources/python/00-databricks-init.py

@@ -75,7 +75,12 @@ def create_and_register_databricks_globals():
     # "table", "sc", "sqlContext" are missing
     spark: SparkSession = DatabricksSession.builder.getOrCreate()
     sql = spark.sql
-    getArgument = dbutils.widgets.getArgument
+
+    # We do this to prevent importing widgets implementation prematurely
+    # The widget import should prompt users to use the implementation
+    # which has ipywidget support.
+    def getArgument(*args, **kwargs):
+        return dbutils.widgets.getArgument(*args, **kwargs)
 
     globals()['dbutils'] = dbutils
     globals()['spark'] = spark