Include the cloud image SBOM generation in the cloud image generation pipeline

[javihernandez]

The description/requirements will be updated after the cloud image generation pipeline is implemented and/or in progress.

[javihernandez]

I have implemented the required bits in the pipeline to generate SBOMs in this branch of the cloud-images-ci-dev repository.
Basically, I updated the pipeline to:

• pull the https://github.com/javihernandez/cloud-images-sbom-tools repository
• collect sbom data from the installed system
• generate final sbom document from the data above
• publish it as an artifact

An example of a successful CI pipeline run can be found here.

I have a created this PR against @jonathanspw's work in progress branch.