[csolution] Add overview: node to *.cbuild.yml files with a reference to the "Overview" MD file specified in the package description file

[jkrech]

Describe The Problem To Be Solved
Allow an IDE to display the "Overview" MarkDown file optionally specified in the "overview=" attribute of the <description> tag in the package description file (*.pdsc)

Suggested Solution
a) Extend the device-pack: node with an overview: subnode in the *cbuild.yml to provide this information.

cbuild:
  device: ARM::SSE-300-MPS3
  device-pack: ARM::[email protected]
    - overview: ${CMSIS_PACK_ROOT}/ARM/V2M_MPS3_SSE_300_BSP/1.5.0/Documents/overview.md
  device-books:
    - name: ${CMSIS_PACK_ROOT}/ARM/V2M_MPS3_SSE_300_BSP/1.5.0/Documents/arm_corstone_sse-300_example_subsystem_technical_reference_manual_101773_0001_03_en.pdf
      title: Arm® SSE-300 - Technical Reference Manual

Extend the board-pack: node accordingly.

b) Add an overview: sub-node to the pack: node similar to path: if an overview is specified for a pack.

 packs:
    - pack: ARM::[email protected]
      path: ${CMSIS_PACK_ROOT}/ARM/CMSIS-FreeRTOS/10.4.6
      overview: ${CMSIS_PACK_ROOT}/ARM/CMSIS-FreeRTOS/10.4.6/docs/overview.md
       :
    - pack: MDK-Packs::[email protected]
      path: ../IoT_Socket

The drawback of a) is that this will not make overview.md files accessible, for Software Packs that are neither Board nor Device packs.
The drawback of b) is that it requires an additional level of indirection to locate the file reference for a device / board.

We could implement a) and b) accepting redundant information in *.cbuild.yml.

[ReinhardKeil]

I suggest to postpone this until the gPRC interface is decided.