Add card number character count validation tests

[okhan-okbay-cko]

What does this PR include?

Automates regression test cases to verify that we check the length of the card number even if it's a valid luhn number and belongs to a scheme.

To test this, some mock luhn numbers of different lengths are created. For example, to test if Visa card number length is being checked by our SDK, I added two different luhn numbers:

440000000002 -> Starts with 4 and consists of 12 digits -> Shows error Please enter a valid card number

4400000000008 -> Starts with 4 and consists of 13 digits -> Does not show error even if it's not a valid Visa card number

Visa cards start with 4 and be between 13, 16 or 19 digits. We can't test the upper character limit because the textfields don't allow us to input more than the max limit.

To increase the testing speed

Rather than relaunching the app each and every time, we only change the card number field. The error we see becomes visible after we tap the Done button on the keyboard, so, it's okay to show or hide that error by tapping that button and verifying our test case and switch to the next one.

1. If current card number after dropping the last 2 characters equals to the previous card number dropping the last character, we get that we're still testing the same card scheme and just delete the last digit and add the new two digits. Refer to the Visa card numbers above to understand this more.

2. When we switch to a new card scheme, we delete all the card number digits and input again.

If you want to understand this flow better, feel free to run the tests locally and watch the behaviour of UI.

When we come across Amex, which has 4 digits of security code, we delete the security code field completely (if security code is different than the previous one)

[ehab-al-cko]

👌