get apple pay certificates only from metadata during the session call

[ShankarSinghC]

Currently we have apple pay certificates being stored in the metadata as well as connector_wallet_details when a merchant connector account is created. During the session call we try to get the certificates from the connector_wallet_details if it fails we try to get it from metadata.

Currently when apple pay certificates are being updated with the merchant connector update call only the metadata is being updated. Because of this connector_wallet_details will still have the old data using which we make the session call.

In order to fix it, this pr contains the changes to get the apple pay certificates from the metadata only as it will have the latest updated data. In subsequent pr mca update inconsistency will be handled.