Add Sqlpackage to MS APT repo or MSSQL image

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**Is your feature request related to a problem? Please describe.**
I've created a custom MSSQL container image to support 2 workflows.

1) Run container without existing database, use DACPAC to create database.
2) Attach an existing database and apply an updated DACPAC.

Sqlpackage is required to do this but not available on the base image or through Microsoft's APT repository.

**Describe the solution you'd like**
Ideally, Sqlpackage would be added to the Microsoft APT repository as an installable package or bundled with other tools like Sqlcmd (/opt/mssql-tools/bin/sqlcmd) in the official MSSQL Docker image.

**Describe alternatives you've considered**
The current workaround to Sqlpackage not being available is to install unzip, download the Sqlpackage zip file from Microsoft's website, extract and set it as executable. This is several lines of abstraction over what could be a simple `RUN apt-get update && apt-get install sqlpackage`

Review the requested packaging targets: the Microsoft APT repository and the official MSSQL Docker image, including the existing /opt/mssql-tools/bin/sqlcmd location. Compare them with the unzip workaround and the proposed apt-get install sqlpackage flow. Done means Sqlpackage is available through an installable APT package or bundled in the official image.

Written by the indexing model from the issue text.