Dashboard: Date filter - update the info popover text

The info popover text for the Date field needs to be updated to be in-line with changes made as part of ERM-1648.

Change from:

The Date can be variable or fixed. For a variable date set the values of the three fields Number, Time unit and When in the first radio button. Use the second radio button to enter a fixed date.

To:

"Date" can be relative or fixed. Choose the third radio button option to filter by a fixed date. To apply a relative date choose either the first option "Today" or the second option and set the values of the three fields: "Length of time", "Unit of time" and "Before or after today".