Features
   * When the new compilation option MBEDTLS_PSA_STATIC_KEY_SLOTS is enabled,
     key store uses static key slot buffers instead of dynamically allocated
     ones.
   * The size of each static key slot buffer is determined by
     MBEDTLS_PSA_STATIC_KEY_SLOT_BUFFER_SIZE. If not set, its default value
     is set to accomodate for the largest PSA asymmetric/symmetric key enabled
     in the build.