This commit introduces major changes in the layers integration steps
performed every time a new MR is opened in one of the BSP repositories.
More in detail:

* Introduces jinja2 templating tool to perform dynamic child pipeline
and dinamically assign the INTEGRATION variable value to the CI jobs.
* The main layers-integration.yml file only contains check and trigger
pipelines to create a dynamic downstream pipeline.
* Introduces layers-integration-jobs.yml that is dinamically assigned
with the variables from the INTEGRATION variable and that executes all
the main tasks of layer integration pipelines