Set a unique correlator query param for each banner ad request

[ishcherba]

Description 🤔

The correlator in Google Ad Manager is the query parameter that tells Ad Manager if you are still on the same screen, so ads should be unique, or if you have moved to a different one, so ads should be different.

We have found that the correlator value is not changing between screens, so the google ad server assumes you are on the same page/screen constantly and requires unique ads. This means that you can 'run out' of ads when you navigate through the app.
These PR changes make the request correlator a random value for each ad request.

Reason for change 🤖

https://economist.atlassian.net/browse/CCA-496

https://economist.atlassian.net/browse/MAPP-1204

Type of change 🧩

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please explain in the description section above)

How have you tested this works? 🧪

Devices / Simulators

I have tested on the following devices and/or simulators.

• iPhone 12
• iPhone 11
• iPhone X
• iPhone SE (2nd Generation)
• iPhone SE (1st Generation)
• iPad (portrait)
• iPad (landscape)
• Android (Samsung)
• Android (Pixel)

I have tested on the following platforms.

• iOS 14
• iOS 13
• iOS 12
• Android 11
• Android 10
• Android 9

Checklist ✔

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have provided details on how I have tested my code
• I have referenced the ticket number above
• I have provided a description of the ticket