The instruction to build debain package doesn't work

**Describe the bug**
Follow https://github.com/Azure/azure-cli/tree/dev/scripts/release/debian to build the debian package. It didn't work. Build failed.

**Additional context**
The instruction is out of date. One build error was related to the trailing `&&`.

https://github.com/Azure/azure-cli/blob/dev/scripts/release/debian/Dockerfile#L31

Even I removed it, the build ran into other issue. I ended up coming up a script following the azure devop pipeline https://github.com/Azure/azure-cli/blob/39774073032f84740272745f816dc81c2d47a448/azure-pipelines.yml#L719.

```
cd azure-cli

mkdir ~/artifacts

BUILD_STAGINGDIRECTORY=~/artifacts scripts/release/pypi/build.sh release

ls -l ~/artifacts

mkdir ~/debian

# focal is ubutun 20.04
DISTRO=focal DISTRO_BASE_IMAGE=ubuntu:focal BUILD_SOURCESDIRECTORY=$(pwd) BUILD_STAGINGDIRECTORY=~/debian SYSTEM_ARTIFACTSDIRECTORY=~/artifacts scripts/release/debian/pipeline.sh

ls -l ~/debian

sudo dpkg -i ~/debian/azure-cli_2.30.0-1~focal_all.deb

az version
```