gitlab-based_packaging_workflow: Link to apertis_packaging_guide

Update some broken links by pointing them to the new location of the
ci-package-builder documentation.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>

content/guides/gitlab-based_packaging_workflow.md

@@ -48,8 +48,9 @@ or enter the `apertis-*-package-source-builder` Docker container:
 # How to manually sync an Apertis package with a new version
 
 Upstream updates are usually handled automatically by the
-[`ci-update-from-upstream.yml`](https://gitlab.apertis.org/infrastructure/ci-package-builder/)
-Continous Integration pipeline, which fetches upstream packages, merges them
+[`ci-package-builder.yml`](https://gitlab.apertis.org/infrastructure/ci-package-builder/)
+Continous Integration pipeline, which
+[fetches upstream packages, merges them]({{< ref "apertis_packaging_guide.md#pulling-updates-or-security-fixes-from-upstream-distributions" >}})
 with the Apertis contents and directly creates Merge Requests to be reviewed by
 [maintainers]({{< ref "contributions.md#the-role-of-maintainers" >}}).
 
@@ -128,10 +129,10 @@ back](https://honk.sigxcpu.org/projects/git-buildpackage/manual-html/gbp.patches
 # How to issue a release
 
 The process for landing downstream changes is documented in the
-[ci-package-builder documentation](https://gitlab.apertis.org/infrastructure/ci-package-builder#landing-downstream-changes-to-the-main-archive).
+[ci-package-builder documentation]({{< ref "apertis_packaging_guide.md#landing-downstream-changes-to-the-main-archive" >}}).
 
 # How to add a new packaging repository
 
 The process for adding new packages from Debian is documented in the
-[ci-package-builder documentation](https://gitlab.apertis.org/infrastructure/ci-package-builder#adding-new-packages-from-debian).
+[ci-package-builder documentation]({{< ref "apertis_packaging_guide.md#adding-new-packages-from-debian" >}}).