Add gradle wrapper validation

[jobarr-amzn]

Issue #, if available: https://github.com/amazon-ion/ion-java/security/code-scanning/16

Description of changes:

We have a spurious "binary artifacts" alert from OSSF scorecard, for gradle-wrapper.jar.

According to ossf/scorecard#2039 this ought to be silenced if we use the gradle/wrapper-validation-action action.

Gradle publishes this workflow to allow validation of gradle wrapper JARs to ensure that they actually are the jars published by Gradle. See: https://github.com/gradle/wrapper-validation-action#add-to-an-existing-workflow

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

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[jobarr-amzn]

From the jdk 17 run above:

Run gradle/wrapper-validation-action@56b90f209b02bf6d1deae490e9ef18b21a389cd4
  with:
    min-wrapper-count: 1
    allow-snapshots: false
✓ Found known Gradle Wrapper JAR files:
  91941f522fbfd4431cf57e445fc3d5200c85f957bda2de5251353cf11174f4b5 gradle/wrapper/gradle-wrapper.jar