{bp-2899} apps: migrate to SPDX identifier

[jerpelea]

Summary

Most tools used for compliance and SBOM generation use SPDX identifiers
This change brings us a step closer to an easy SBOM generation.

Impact

RELEASE

Testing

CI

[nuttxpr]

[Experimental Bot, please feedback here]

No, this PR does not fully meet the NuttX requirements. While it provides a summary of the change, it lacks crucial details:

• Insufficient Summary Detail: The summary explains the "why" but not the "what" or "how". Which files are changed? How are SPDX identifiers being added? What tools are being targeted?
• Missing Impact Assessment: "RELEASE" is not a sufficient impact assessment. Each impact category (user, build, hardware, documentation, security, compatibility) needs a NO/YES answer and description if YES. Even if the answer is NO for all, it should be explicitly stated.
• Inadequate Testing Information: "CI" is insufficient. While CI testing is important, it doesn't replace the need for specific local testing details. The PR needs to specify the host OS, CPU, compiler, target architecture, board, and configuration used for testing. Crucially, it's missing the actual testing logs before and after the change to demonstrate the impact and verify the fix.

The PR needs to be significantly expanded to meet the requirements. It should provide specific details for each section, including concrete examples and evidence of testing.