[DOC] SBOM is missing ExternalRef (CPE) since 11.3.0 releases

[SR4ven]

Describe the issue
The SBOMs of 11.3.0 and newer are missing the ExternalRef field in the SBOM containing the cpe identifier.

Reference
With cpe:
https://github.com/FreeRTOS/FreeRTOS-Kernel/blob/V11.2.0/sbom.spdx
Without cpe:
https://github.com/FreeRTOS/FreeRTOS-Kernel/blob/V11.3.0/FreeRTOS-Kernel-V11.3.0-repository-SPDX2.3.spdx

Side node:
A fix filename for the SBOM which doesn't contain the release version string would be easier to parse with scripts.