Allow setting of default value for donation amount or membership fee via url for contribution/membership pages

Allow advanced users to set the default value for donation amount and membership fee via URL
Internally all the donation amount and membership fees are price sets.
Here is the example for setting defaults
<site-name>/civicrm/contribute/transact?reset=1&id=1&price_2=3

Here were are setting price set field = 2 with value 3 as default