Override the setup_future_usage field to on_session based on merchant config

[ShankarSinghC]

This is the use case where in which we need if the setup_future_usage is set to off_session in the payment method needs to be just saved at hyperswitch and not at connector.

skip_saving_wallet_at_connector_<merchant_id> is the config which takes vector of payment method type as the value. When this config is set, the setup_future_usage is overridden to on_session by which mandates won't be created at the connector's end.

curl --location 'localhost:8080/configs/' \
--header 'api-key: test_admin' \
--header 'Content-Type: application/json' \
--data '{
    "key": "skip_saving_wallet_at_connector_merchant_1718351667",
    "value": "[\"apple_pay\"]"
}'

Also add a validation to add duplicate apple pay payment method being saved.