Automate non-Javadoc multi-line comments for license headers

https://github.com/micrometer-metrics/micrometer/pull/2940 changed license headers to non-Javadoc multi-line comments (thanks @izeye 🚀). This issue is for adding the same style to the license plugin config so that license-related tasks (`licenseFormat`, `licenseCheck`) works the same way.

Related: https://github.com/micrometer-metrics/micrometer/issues/2412