This is a workaround for MSHADE-148, which leads to an infinite loop when building Spark with maven 3.3.x. This was originally caused by #6441, which added a bunch of test dependencies on the spark-core test module. Recently, it was revealed by #7193.

This patch adds a `-Prelease` profile. If present, it will set `createDependencyReducedPom` to true. The consequences are:
- If you are releasing Spark with this profile, you are fine as long as you use maven 3.2.x or before.
- If you are releasing Spark without this profile, you will run into SPARK-8781.
- If you are not releasing Spark but you are using this profile, you may run into SPARK-8819.
- If you are not releasing Spark and you did not include this profile, you are fine.

This is all documented in `pom.xml` and tested locally with both versions of maven.

Author: Andrew Or <andrew@databricks.com>

Closes #7219 from andrewor14/fix-maven-build and squashes the following commits:

1d37e87 [Andrew Or] Merge branch 'master' of github.com:apache/spark into fix-maven-build
3574ae4 [Andrew Or] Review comments
f39199c [Andrew Or] Create a -Prelease profile that flags `createDependencyReducedPom`