[Explore] Redirect to Gpay & Back with data

[pocha]

We need functionality where the user can come to Kilvish, click on a pay button which launches a UPI app & then post payment, gets redirected back to Kilvish with payment screenshot & amount. This issue to explore the same.

Steps

• Setup the app. Go through the app flow - registration, home & detail screen. Also, sharing an image to the app will open handle_share screen with the image shown
• The Add Expense button on Home screen should be changed to Pay & it should launch Gpay
• Once payment is done in Gpay, the control should come back to the app & handle_share screen should show with the image of the payment transaction done.

[pocha]

@Ruchi71 I am perfectly fine with using platform specific code in flutter. Eg platform.invokeMethod('getBatteryLevel') invokes the android specific getBatteryLevel() function

The gpay launch code in Android

How to launch an android activity & then return result as mentioned here . This is a bit tricky as we dont know what gpay implements & hope for it that it will return. This part need testing.