Block automatic sync from debian for the next LTS

Upstream haproxy has the concept of an LTS release, and a stable (non-LTS) release. Currently, these are (see table at http://www.haproxy.org/):

stable: 2.1.x
stable LTS: 2.0.x

Debian unstable is at the moment tracking 2.0.x, and debian experimental is tracking 2.1.x.

For the next ubuntu lts release, we would like to stay on the 2.0.x track, which is upstream's LTS.

From the 2.0 upstream announcement[2]:
"""
The development will go on with 2.1 which will not be LTS, so it will
experience quite some breakage to prepare 2.2 which will be LTS and
expected approximately at the same date next year.
"""

"same date next year" would be roughly June 2020, so not in time for Ubuntu 20.04.

Since this package is a sync, whenever the debian maintainers decide to push 2.1.x into unstable, we will automatically sync it (if we are not yet in feature freeze mode). To avoid that, a few options were explored[1], and adding an ubuntu version to the package seems the best one.

Therefore, the package will have an ubuntu version, have its maintainer changed, but no extra delta, just to stop the automatic sync from happening. Whenever new versions of the 2.0.x track are uploaded to debian/sid, we will merge it manually into ubuntu.

1. https://lists.ubuntu.com/archives/ubuntu-devel/2019-December/040853.html
2. https://<email address hidden>/msg34215.html