Integrate gitlab-ci/share-yaml-code-for-manifest-integration and 2 more

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Commit: seco-ne/yocto/infrastructure/gitlab-ci@686323c6

Remove yaml redundancies in manifest-integration

Leave all common yaml parts in manifest-integration.yml and add
manifest-integration-yocto.yml and manifest-integration-ci-test.yml
containing the different variable assignments for each environment.

The repos including these files have to be updated with the new names.

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Commit: seco-ne/yocto/infrastructure/gitlab-ci@4c751096

Harmonize manifest-integration yaml files for yocto and ci-test

This is the first step for reducing code duplicates.

BCS 746-000807

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Commit: seco-ne/yocto/infrastructure/gitlab-ci@c877f9c9

retrigger: Allow to specify the manifest's remote identifier in a variable

Costum manifest may override this variable