Integrate gitlab-ci/fix-remote-name-on-retrigger and 1 more

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Commit: seco-ne/yocto/infrastructure/gitlab-ci@c917791b

Fix remote name on retrigger stage

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Commit: seco-ne/yocto/infrastructure/gitlab-ci@1ba52853

Move repositories to git.seco.com

Rename variable JENKINSGUF_SSH_PRIVATE_KEY / SSH_PRIVATE_KEY to
GITLAB_PRIVATE_KEY on this occasion, because it contains a private key
that was generated exclusively for this use case. The according public
key has been added as a deploy key in GitLab to all repositories that
this repository needs access to.

Add more detailed documentation concerning this configurationdirectly in
the gitlab-ci files.