Adds optional callback to env.get in function node

[knolleary]

Adds optional callback to env.get in function node so that it can get jsonata properties in the future.

[Steve-Mcl]

Looks good to me.

I would suggest we also update the function node d.ts so that editor intelisense offers the alternative sig.
packages/node_modules/@node-red/editor-client/src/types/node-red/func.d.ts

declare class env {
    /** 
     * Get an environment variable value  
     * 
     * Predefined node-red variables...  
     *   * `NR_NODE_ID` - the ID of the node
     *   * `NR_NODE_NAME` - the Name of the node
     *   * `NR_NODE_PATH` - the Path of the node
     *   * `NR_GROUP_ID` - the ID of the containing group
     *   * `NR_GROUP_NAME` - the Name of the containing group
     *   * `NR_FLOW_ID` - the ID of the flow the node is on
     *   * `NR_FLOW_NAME` - the Name of the flow the node is on
     * @param name Name of the environment variable to get
     * @example 
     * ```const flowName = env.get("NR_FLOW_NAME");```
     */
    static get(name:string) :any;
    /** 
     * Get an environment variable value (asynchronous).
     * 
     * Predefined node-red variables...  
     *   * `NR_NODE_ID` - the ID of the node
     *   * `NR_NODE_NAME` - the Name of the node
     *   * `NR_NODE_PATH` - the Path of the node
     *   * `NR_GROUP_ID` - the ID of the containing group
     *   * `NR_GROUP_NAME` - the Name of the containing group
     *   * `NR_FLOW_ID` - the ID of the flow the node is on
     *   * `NR_FLOW_NAME` - the Name of the flow the node is on
     * @param name Name of the environment variable to get
     * @param callback Callback function (`(err,value) => {}`)
     * @example 
     * ```const flowName = env.get("NR_FLOW_NAME");```
     */
    static get(name:string, callback: Function) :void;
}

I will also raise an issue to bake this into the nr monaco editor repo so we have this for future monaco version updates.

[knolleary]

Types updated.