docs: replace --skip-build with --skip-validation in app-management (#373)

The `databricks apps deploy --skip-build` flag has been replaced with
`--skip-validation`. Update the example and description in the app
management docs to reflect the current CLI flag.

Signed-off-by: Tony Dang <tony@tonydang.com>

Author: thisistonydang

docs/docs/app-management.mdx

@@ -56,10 +56,10 @@ databricks apps deploy --help
     databricks apps deploy --var="warehouse_id=abc123"
     ```
 
-- Skip the build step for faster iteration:
+- Skip validation for faster iteration:
 
     ```bash
-    databricks apps deploy --skip-build
+    databricks apps deploy --skip-validation
     ```
 
 - Force deploy (override Git branch validation):