Support for Gradle's configuration cache

[birukoff]

If you enable Gradle's configuration cache, an attempt to build an RPM fails with message

5 problems were found storing the configuration cache, 1 of which seems unique.
- Task `:foo:bar` of type `com.netflix.gradle.plugins.rpm.Rpm`: invocation of 'Task.project' at execution time is unsupported.
  See https://docs.gradle.org/6.7/userguide/configuration_cache.html#config_cache:requirements:use_project_during_execution

Please, add support for configuration cache.