Drop support for Java 8, because some vulnerabilities can no longer be resolved with Java 8; make Java 17 the lowest supported version

[janblom]

Is your feature request related to a problem? Please describe.
For some dependencies, no updates are released that are compatible with Java 8. This forces known vulnerabilities to be included in the distribution of the Rabbit Tools. To avoid this undesirable situation, the minimum required version of Java to be used to run the Rabbit Tools should be set to higher version, preferably Java 17.

This issue also serves as a heads-up to organizations that still (need to) use a Java version lower than 17.

Describe the solution you'd like
Define Java 17 as the minimum version that a compiled version of the Rabbit Tools can be run with.

Describe alternatives you've considered
We could go for Java 11 for now, but since Java 11 has already reached end of life, this does not seem to make a lot of sense: it will only lead to having to make an extra upgrade step, maybe soon.
Someone needing the Rabbit Tools with a Java version lower than 17 could always compile the tools themselves.

Additional context
While preparing for a maintenance release, for which we routinely upgrade dependencies to the latest available minor version,
we noted we had to exclude some dependencies, as there is no longer a recent enough version of some dependencies available that support Java 8. This has been the case for some test dependencies for a longer period already, which was resolved by setting the minimum Java version that WhiteRabbit and RabbitInAHat can be built with to Java 17.
While Java 8 is likely to be supported to some extent for a while longer, it becomes less and less viable as a healthy baseline version, because we can expect the number of dependencies that have no Java 8 support to increase.