Integrate gitlab-ci/add-confluence-stage and 2 more

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Commit: seco-ne/yocto/infrastructure/gitlab-ci@f8c1d732

Add confluence stage

This adds two jobs to the Yocto pipeline:

 - generate-confluence-page
 - publish-confluence-page

The first one generates a confluence page from a template
(`confluence-page.xml.jinja2`) using information downloaded from all
successful "Deploy FTP" jobs of the same pipeline.

The second one publishes this page in Confluence and displays a link to
the new page. If the page already exists it is overwritten.

The place in Confluence where the new page is published is configurable
via the `CONFLUENCE_SPACE` and `CONFLUENCE_PARENT_ID` variables.

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Commit: seco-ne/yocto/infrastructure/gitlab-ci@fee9493b

generate-build-pipeline: re-add YAML format parsing

This was accidentally forgotten in the previous commit.

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Commit: seco-ne/yocto/infrastructure/gitlab-ci@9b777f29

Rename "generate_job_from_template" script to "render_jinja2_template"

This makes the script more general and open for other future purposes.
The parsing of the YAML content is conditional now, depending on the new
"format" argument.