docs: Use the YAML multi-line indicator (#11552)

In the Spark Quickstart guide, the initial docker-compose example specifies an
entrypoint script in a multi-line string. The string is mistakenly started with
the 'folded style' indicator `>`, which causes formatters to collapse it into
one line.

Changing to the 'literal style' indicator `|` resolves the issue and preserves
formatting.

Folded Style: <https://yaml.org/spec/1.2.2/#813-folded-style>
Literal Style: <https://yaml.org/spec/1.2.2/#812-literal-style>

Co-authored-by: Neodon <github.com/apache/[email protected]>

site/docs/spark-quickstart.md

@@ -100,7 +100,7 @@ services:
       - AWS_ACCESS_KEY_ID=admin
       - AWS_SECRET_ACCESS_KEY=password
       - AWS_REGION=us-east-1
-    entrypoint: >
+    entrypoint: |
       /bin/sh -c "
       until (/usr/bin/mc config host add minio http://minio:9000 admin password) do echo '...waiting...' && sleep 1; done;
       /usr/bin/mc rm -r --force minio/warehouse;