Add `default` attribute to the device memory in .cbuild-run.yml

[TeoMahnic]

Describe The Problem To Be Solved
The CMSIS-Pack specification defines a default attribute for memory elements, indicating a general purpose memory region that does not require special handling. This attribute is currently not exposed in the .cbuild-run.yml under the system-resources: memory node.

Use Case
RTT control block search in pyOCD requires identifying default memory regions, which is currently not possible without this attribute.