springboot Enhance bomr to handle Kotlin version upgrades

The version is defined in gradle.properties as it's used in multiple places. This causes bomr to fail:

> Task :spring-boot-project:spring-boot-dependencies:bomrUpgrade
Upgrade to Dropwizard Metrics 4.1.5
Upgrade to Jackson Bom 2.10.3
Upgrade to Jersey 2.30.1
Upgrade to Jetty 9.4.27.v20200227
Upgrade to Kotlin 1.3.70

> Task :spring-boot-project:spring-boot-dependencies:bomrUpgrade FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':spring-boot-project:spring-boot-dependencies:bomrUpgrade'.
> git commit failed

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 2m 39s
1 actionable task: 1 executed