[OB3] Open banking identity cache expiry time is not modifiable

[imesh94]

According to the IS open-banking.xml.j2, following configuration in the deployment.toml should allow to modify the open banking identity cache expiry time.

[open_banking.identity.cache]
cache_access_expiry_minutes=15
cache_modified_expiry_minutes=15

But currently this configuration is not read properly by the OpenBankingConfigurationService, and the default expiry time (60 minutes) cannot be changed.