Gets the previous dynamic page URL.
The getPreviousDynamicPage() function can only be called on a dynamic page
dataset.
The function returns a Promise that's resolved to the relative URL of the
previous dynamic page or null if there is no previous page.
The previous page is determined by the lexicographical order of the dynamic page relative URLs. You can see all of the relative URLs for a dynamic page by viewing the collection connected to the page.
URLs for items that don't match the dataset's filters aren't returned.
For example, consider the following situation:
If Bob is not an active employee, when you call getPreviousDynamicPage()
from Cathy's page, the returned Promise will resolve to "employees/Alice".
Pass the returned URL to the to() function to
navigate to the previous dynamic page.