Add default configuration for Xmx

**Is your feature request related to a problem? Please describe.**

By default, certain Java versions assume heap should consume all the available memory, so apps should limit the RAM.

**Describe the solution you'd like**

`applicationDefaultJvmArgs=...-Xmx512m...`

See https://docs.gradle.org/current/userguide/application_plugin.html

**Describe alternatives you've considered**

Adding `maxHeapSize` (or `jvmArg`) option to `allure-gradle` plugin.
It won't help for those who call `allure` commandline directly.

**Additional context**

allure-gradle tests fail with OOM: https://github.com/allure-framework/allure-gradle/pull/94

Start with the applicationDefaultJvmArgs configuration described in the Gradle application plugin documentation and inspect the allure-gradle tests referenced in the issue. Confirm how the Allure command-line entry point receives its JVM arguments and verify that the default Xmx512m limit prevents the reported OOM failures without requiring a separate plugin option.

Written by the indexing model from the issue text.