[SPARK-14421] Upgrades protobuf dependency to 2.6.1 for the new version of KCL, and…

## What changes were proposed in this pull request?

When running with Kinesis Consumer Library (KCL), against a stream that contains aggregated data, the KCL needs access to protobuf to de-aggregate the records.   Without this patch, that results in the following error message:

```
   Caused by: java.lang.ClassNotFoundException: com.google.protobuf.ProtocolStringList
```

This PR upgrades the protobuf dependency within the kinesis-asl-assembly, and relocates that package (as not to conflict with Spark's use of 2.5.0), which fixes the above CNFE.

## How was this patch tested?

Used kinesis word count example against a stream containing aggregated data.

See: SPARK-14421

Author: Brian O'Neill <bone@alumni.brown.edu>

Closes #13054 from boneill42/protobuf-relocation-for-kcl.

external/kinesis-asl-assembly/pom.xml

@@ -63,7 +63,12 @@
     <dependency>
       <groupId>com.google.protobuf</groupId>
       <artifactId>protobuf-java</artifactId>
-      <scope>provided</scope>
+      <version>2.6.1</version>
+      <!-- 
+         We are being explicit about version here and overriding the 
+         spark default of 2.5.0 because KCL appears to have introduced 
+         a dependency on protobuf 2.6.1 somewhere between KCL 1.4.0 and 1.6.1.
+       -->
     </dependency>
     <dependency>
       <groupId>org.glassfish.jersey.core</groupId>
@@ -147,6 +152,15 @@
             <include>*:*</include>
           </includes>
         </artifactSet>
+        <relocations>
+          <relocation>
+            <pattern>com.google.protobuf</pattern>
+            <shadedPattern>kinesis.protobuf</shadedPattern>
+            <includes>
+              <include>com.google.protobuf.**</include>
+            </includes>
+          </relocation>
+        </relocations>
         <filters>
           <filter>
             <artifact>*:*</artifact>