Play Framework

chore: scaffold gradle.properties with config cache enabled (PF-90)

Every fresh app was getting the \"Consider enabling configuration cache
to speed up this build\" nag on every gradle invocation because
playNewApp wasn't writing a gradle.properties.

The play-gradle-plugin has been config-cache safe since Phase 1
(every task uses @Inject services + Property inputs, no Task.project
at execution time). And /opt/play1 already opts in via its own
gradle.properties (per chore commit cd2ea12bf). New apps should
inherit the same default.

Verified: fresh playNewApp now ships gradle.properties with
org.gradle.configuration-cache=true. 1st task run stores the cache
entry, 2nd reuses it (~3x faster). Nag line gone from all output.

Becomes the only mode in Gradle 10, so this also future-proofs new
apps for that upgrade.