[jvm] Gradle cache and parallel builds

[varlanv]

Currently, Gradle optimization features org.gradle.caching and org.gradle.parallel are not enabled.

Is there an issue that prevents to enable them by default?

When I add:

org.gradle.caching=true
org.gradle.parallel=true

and run gradle clean build, everything seems to be okay.

[nedtwigg]

Spotless had intermittent problems with caching (not on first run, but subsequent runs).

https://github.com/diffplug/selfie/blob/75eaaec8cb097d255fde6f46addfa5146ca3a11f/jvm/settings.gradle#L11

But that's fixed in the latest 7.x series. Seems like renovate has stopped working for us...

https://github.com/diffplug/selfie/blob/75eaaec8cb097d255fde6f46addfa5146ca3a11f/renovate.json

I'd be happy to instamerge a PR that enables caching and parallel, but we need a PR that bumps at least Spotless first, bumping any/all other build deps is fine too.