rest-utils uses vulnerable version of hibernate-validator

**Description**
I checked confluent kafka 5.5.1 distribution with WhiteSource and find out that rest-utils uses vulnerable library:
- hibernate-validator-6.0.17.Final.jar has CVE-2019-10219 and CVE-2020-10693 vulnerabilities. The way to fix it is to upgrade to org.hibernate.validator:hibernate-validator:6.0.20.Final

**To Reproduce**
Download Confluent Kafka 5.5.1 distribution (for example `curl -O http://packages.confluent.io/archive/5.5/confluent-community-5.5.1-2.12.tar.gz`)
Open share/java/rest-utils folder in it and find hibernate-validator-6.0.17.Final.jar

**Expected behavior**

- hibernate-validator upgraded to 6.0.20.Final or higher

**Actual behaviour**

- hibernate-validator is 6.0.17.Final