message: Monitoring: Fix JS warnings when updating some silence form fields
  These `onChange` event handlers are actually called with 2 arguments,
  which was causing React to warn that `State updates from the useState()
  and useReducer() Hooks don't support the second callback argument.`
diff: @@ -1421,7 +1421,11 @@ const SilenceForm_: React.FC<SilenceFormProps> = ({ defaults, Info, title }) =>
  {isStartNow ? (
  <DatetimeTextInput isDisabled value="Now" />
  ) : (
  - <DatetimeTextInput isRequired onChange={setStartsAt} value={startsAt} />
  + <DatetimeTextInput
  + isRequired
  + onChange={(v: string) => setStartsAt(v)}
  + value={startsAt}
  + />
  )}
  </div>
  <div className="col-xs-2">
  @@ -1429,14 +1433,18 @@ const SilenceForm_: React.FC<SilenceFormProps> = ({ defaults, Info, title }) =>
  <Dropdown
  dropDownClassName="dropdown--full-width"
  items={durationItems}
  - onChange={setDuration}
  + onChange={(v: string) => setDuration(v)}
  selectedKey={duration}
  />
  </div>
  <div className="col-xs-5">
  <label>Until...</label>
  {duration === durationOff ? (
  - <DatetimeTextInput isRequired onChange={setEndsAt} value={endsAt} />
  + <DatetimeTextInput
  + isRequired
  + onChange={(v: string) => setEndsAt(v)}
  + value={endsAt}
  + />
  ) : (
  <DatetimeTextInput
  isDisabled
  @@ -1547,11 +1555,20 @@ const SilenceForm_: React.FC<SilenceFormProps> = ({ defaults, Info, title }) =>
  <SectionHeading text="Info" />
  <div className="form-group">
  <label>Creator</label>
  - <TextInput aria-label="Creator" onChange={setCreatedBy} value={createdBy} />
  + <TextInput
  + aria-label="Creator"
  + onChange={(v: string) => setCreatedBy(v)}
  + value={createdBy}
  + />
  </div>
  <div className="form-group">
  <label className="co-required">Comment</label>
  - <TextArea aria-label="Comment" isRequired onChange={setComment} value={comment} />
  + <TextArea
  + aria-label="Comment"
  + isRequired
  + onChange={(v: string) => setComment(v)}
  + value={comment}
  + />
  </div>
  </div>
  </div>
  