Add nickname field to SlackConfig form

ui/src/kapacitor/components/config/SlackConfig.tsx

@@ -47,6 +47,18 @@ class SlackConfig extends PureComponent<Props, State> {
 
     return (
       <form onSubmit={this.handleSubmit}>
+        <div className="form-group col-xs-12">
+          <label htmlFor="nickname">Nickname this Configuration</label>
+          <input
+            className="form-control"
+            id="nickname"
+            type="text"
+            placeholder="Optional unless multiple Slack configurations exist"
+            // ref={r => (this.channel = r)}
+            defaultValue={channel || ''}
+            onChange={this.disableTest}
+          />
+        </div>
         <div className="form-group col-xs-12">
           <label htmlFor="slack-url">
             Slack Webhook URL (