Move assertions to a separate artifact

[vlsi]

JUnit5 api ships with Assertions and Assumptions, and it does not provide users with a way to opt-out of those classes.

It would be great if the assertion and assumption classes were moved to a separate artifact.

[sbrannen]

This has been requested before and declined.

• Separate the assertion utility API from the test framework API #2725

However, I'm leaving this open for the time being to allow the team to discuss the topic once again in light of the upcoming JUnit 6.0.

[mpkorstanje]

One argument I'd like to put on the scale is that if I wanted to use JUnit's basic assertions in Cucumber I'd have to add a dependency on junit-jupiter-api while otherwise not using any part of Jupiter.