Consider minimization on shaded jars

Some of our modules shade and relocate Guava as part of their build, this adds a considerable amount to their file size, even though they do not use every single class in Guava's jar.
maven shade-plugin solves this by minimization which only shades classes which are in use in the module into the jar.

There are a few issues with configuring minimzation for our shaded modules currently:

1. There is a bug in shade-plugin where if minimization is declared on a project with pom packaging it fails. I have created a [ticket](https://issues.apache.org/jira/browse/MSHADE-253) and [PR](https://github.com/apache/maven-plugins/pull/107) with a fix for this but could take a while before it is available to us (The fix has been merged but not released yet).
2. Minimization on all of our modules adds a significant amount of build time, which we wish to avoid. (Up from 02:30 mins for a build of the entire project (skipping tests) on a Macbook pro laptop to over 5 mins)

Imported from Jira [BEAM-1720](https://issues.apache.org/jira/browse/BEAM-1720). Original Jira may contain additional context.
Reported by: aviemzur.

No repository file or test is named. Start by reviewing the Maven configurations for the shaded modules and the Maven Shade Plugin minimization limitation, including MSHADE-253 and PR 107; done means reducing unused Guava content without an unacceptable build-time increase.

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