Added MSET command

MSET command added. Requires all keys to have the same JSON Path, which might fit most use cases, but is a limitation.  Optionally we could make the path an array as well to support all use cases.

packages/json/lib/commands/MSET.ts

@@ -0,0 +1,24 @@
+import { RedisJSON, transformRedisJsonArgument } from ".";
+
+export const FIRST_KEY_INDEX = 1;
+
+export function transformArguments(
+    keys: Array<string>,
+    path: string,
+    json: Array<RedisJSON>
+): Array<string> {
+    
+    if (keys.length != json.length)
+        throw new Error("Number of keys and json objects must be equal");
+
+    let args: Array<string> = ["JSON.SET"];
+
+    // walk through the key array, adding the key, the path and the json objects, calling transformRedisJsonArgument for each
+    for (let i = 0; i < keys.length; i++) {
+        args.push(keys[i], path, transformRedisJsonArgument(json[i]));
+    }
+
+    return args;
+}
+
+export declare function transformReply(): "OK" | null;