[ upstream commit 70676ec2c0f50074238b9da9edbe5b38a8f3544d ]

With "make render-docs-live-preview", we use the cilium/docs-builder
image to build a preview of the documentation, to serve it locally, and
to watch the source files for changes to update automatically the
preview.

When the Docker image is present locally, the command uses it. When this
is not the case, it pulls it from Docker, in its ":latest" version by
default. This can be an issue due to commit 0da7224218ab ("ci: pin down
image for documentation workflow"), where we pinned down the
docs-builder image to use in the CI. Since this commit, the reference
image is not longer ":latest", but the tag in use in the CI files. As a
consequence, the live preview may attempt to use an outdated version of
the image. This is currently the case: running the command with no local
image raises an error about a missing "myst_parser" extension, which is
not present on the version tagged with ":latest".

To fix this, we mark builder-image as a dependency for the
render-docs-live-preview target, so that the image gets built locally.

Reported-by: Yoyo Wu <yoyo19980720@163.com>
Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Gilberto Bertin <jibi@cilium.io>