Add GitHub Action validating Gradle wrapper

[valfirst]

Change list

See: https://github.com/gradle/wrapper-validation-action

Types of changes

What types of changes are you proposing/introducing to Java client?
Put an x in the boxes that apply

• No changes in production code.
• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Details

Please provide more details about changes if it is necessary. If there are new features you can provide code samples which show the way they
work and possible use cases. Also you can create gists with pasted java code samples or put them here using markdown.
About markdown please read Mastering markdown and Writing on GitHub

[mykola-mokhnach]

in test we trust ;)