[Docs][Packaging] Documentation to build linux-packaging is outdated

[raulcd]

Describe the bug, including details regarding any error messages, version, and platform.

I am trying to fix some minor issues on the linux-packaging due to the CMake version upgrade PR and I wasn't able to find updated documentation on how to test locally. Testing via CI is slow and error prone. The documentation here should be updated:
https://github.com/apache/arrow/tree/main/dev/tasks/linux-packages#how-to-build-deb-packages

If I try the current docs it fails with:

$ rake version:update
apt-dists-merge is needed for apt:* tasks
cd apache-arrow
/usr/bin/ruby3.2 -S rake version:update
cd /home/raulcd/code/arrow/dev/tasks/linux-packages/../../..
cd -
cd apache-arrow-apt-source
/usr/bin/ruby3.2 -S rake version:update
cd /home/raulcd/code/arrow/dev/tasks/linux-packages/../../..
cd -
cd apache-arrow-release
/usr/bin/ruby3.2 -S rake version:update
cd /home/raulcd/code/arrow/dev/tasks/linux-packages/../../..
cd -
$ rake apt
apt-dists-merge is needed for apt:* tasks

It would be nice to add to the docs how to target specific linux packages to be build too by setting the environment variables.
Based on workflows on CI it seems we do the following:

      - name: Build
        run: |
          set -e
          pushd arrow/dev/tasks/linux-packages
          rake version:update ARROW_RELEASE_TIME="$(date --iso-8601=seconds)"
          rake docker:pull || :
          rake --trace apt:build BUILD_DIR=build
          popd
        env:
          APT_TARGETS: ubuntu-focal
          ARROW_VERSION: 20.0.0.dev66
          REPO: ${{ secrets.REPO }}
          YUM_TARGETS: ubuntu-focal

Component(s)

Packaging, Documentation

[kou]

Ah, sorry. We need gem install apt-dists-merge.

[raulcd]

but it is not required for APT_TARGETS=ubunut-focal rake --trace apt:build BUILD_DIR=build
I was able to run that locally without requiring apt-dists-merge

[raulcd]

Issue resolved by pull request 45481
#45481