[docs] Add missing JavaDocs (#6146)

cameraserver/src/main/java/edu/wpi/first/cameraserver/CameraServer.java

@@ -39,6 +39,7 @@ import java.util.concurrent.atomic.AtomicInteger;
  * NetworkTables.
  */
 public final class CameraServer {
+  /** CameraServer base port. */
   public static final int kBasePort = 1181;
 
   private static final String kPublishName = "/CameraPublisher";

cameraserver/src/main/java/edu/wpi/first/cameraserver/CameraServerShared.java

@@ -4,6 +4,7 @@
 
 package edu.wpi.first.cameraserver;
 
+/** CameraServer shared functions. */
 public interface CameraServerShared {
   /**
    * get the main thread id func.

cameraserver/src/main/java/edu/wpi/first/cameraserver/CameraServerSharedStore.java

@@ -4,6 +4,7 @@
 
 package edu.wpi.first.cameraserver;
 
+/** Storage for CameraServerShared instance. */
 public final class CameraServerSharedStore {
   private static CameraServerShared cameraServerShared;