use create if not exist method for cleaner syntax (cloudflare#22814)

Author: Light2Dark

src/content/docs/r2/data-catalog/get-started.mdx

@@ -171,7 +171,6 @@ We will use [marimo](https://github.com/marimo-team/marimo) as a Python notebook
         		import pyarrow.parquet as pq
 
         		from pyiceberg.catalog.rest import RestCatalog
-        		from pyiceberg.exceptions import NamespaceAlreadyExistsError
 
         		# Define catalog connection details (replace variables)
         		WAREHOUSE = "<WAREHOUSE>"
@@ -187,7 +186,6 @@ We will use [marimo](https://github.com/marimo-team/marimo) as a Python notebook
         		)
         		return (
         				CATALOG_URI,
-        				NamespaceAlreadyExistsError,
         				RestCatalog,
         				TOKEN,
         				WAREHOUSE,
@@ -200,12 +198,9 @@ We will use [marimo](https://github.com/marimo-team/marimo) as a Python notebook
 
 
         @app.cell
-        def _(NamespaceAlreadyExistsError, catalog):
+        def _(catalog):
         		# Create default namespace if needed
-        		try:
-        				catalog.create_namespace("default")
-        		except NamespaceAlreadyExistsError:
-        				pass
+        		catalog.create_namespace_if_not_exists("default")
         		return