[MINOR][DOCS] Clarify that Spark apps should mark Spark as a 'provided' dependency, not package it

## What changes were proposed in this pull request?

Spark apps do not need to package Spark. In fact it can cause problems in some cases. Our examples should show depending on Spark as a 'provided' dependency.

Packaging Spark makes the app much bigger by tens of megabytes. It can also bring in conflicting dependencies that wouldn't otherwise be a problem. https://issues.apache.org/jira/browse/SPARK-26146 was what reminded me of this.

## How was this patch tested?

Doc build

Closes apache#23938 from srowen/Provided.

Authored-by: Sean Owen <[email protected]>
Signed-off-by: Sean Owen <[email protected]>

Author: srowen

docs/cloud-integration.md

@@ -87,6 +87,7 @@ is set to the chosen version of Spark:
     <groupId>org.apache.spark</groupId>
     <artifactId>hadoop-cloud_{{site.SCALA_BINARY_VERSION}}</artifactId>
     <version>${spark.version}</version>
+    <scope>provided</scope>
   </dependency>
   ...
 </dependencyManagement>

docs/quick-start.md

@@ -341,6 +341,7 @@ Note that Spark artifacts are tagged with a Scala version.
       <groupId>org.apache.spark</groupId>
       <artifactId>spark-sql_{{site.SCALA_BINARY_VERSION}}</artifactId>
       <version>{{site.SPARK_VERSION}}</version>
+      <scope>provided</scope>
     </dependency>
   </dependencies>
 </project>

docs/streaming-programming-guide.md

@@ -385,11 +385,12 @@ Similar to Spark, Spark Streaming is available through Maven Central. To write y
         <groupId>org.apache.spark</groupId>
         <artifactId>spark-streaming_{{site.SCALA_BINARY_VERSION}}</artifactId>
         <version>{{site.SPARK_VERSION}}</version>
+        <scope>provided</scope>
     </dependency>
 </div>
 <div data-lang="SBT" markdown="1">
 
-	libraryDependencies += "org.apache.spark" % "spark-streaming_{{site.SCALA_BINARY_VERSION}}" % "{{site.SPARK_VERSION}}"
+	libraryDependencies += "org.apache.spark" % "spark-streaming_{{site.SCALA_BINARY_VERSION}}" % "{{site.SPARK_VERSION}}" % "provided"
 </div>
 </div>