Java linter defaults to sun style checks

[yuriylesyuk]

This ruleset is highly restrictive and insists on 80 columns line limit, which is counter-productive.

- Using [checkstyle v9.0.1] https://checkstyle.sourceforge.io
9113- Mega-Linter key: [JAVA_CHECKSTYLE]
9114- Rules config: [sun_checks.xml]

we need to switch to the google style set.

as a further incremental improvement, we can configure a google rule set from a google repository.

https://github.com/googleapis/google-api-java-client/blob/main/checkstyle.xml

We also would need to discuss and finetune specific rules.
Two I've encountered with not helpful defaults:

Error: /github/workspace/references/hashicorp-vault-integration/vault-facade-callout/src/main/java/com/exco/vaultkeystojwks/VaultKeysToJwks.java:77:3: Comment matches to-do format 'TODO:'. [TodoComment]

https://checkstyle.sourceforge.io/apidocs/com/puppycrawl/tools/checkstyle/checks/coding/HiddenFieldCheck.html

we are going to hit more in the future, thus it is better to be ready for it and have a process in place.