docs(js): Update default value for deleteSourcemapsAfterUpload to true (#14319)

Author: chargome

docs/platforms/javascript/guides/nextjs/configuration/build/index.mdx

@@ -114,7 +114,7 @@ A glob or an array of globs that specifies which build artifacts should not be u
 
 </SdkOption>
 
-<SdkOption name="sourcemaps.deleteSourcemapsAfterUpload" type="boolean" defaultValue="false">
+<SdkOption name="sourcemaps.deleteSourcemapsAfterUpload" type="boolean" defaultValue="true">
 
 Toggle whether generated source maps within your Next.js build folder should be automatically deleted after being uploaded to Sentry.