Gradle Wrapper Validation

[oguzkocer]

In Automattic/a8c-ci-toolkit-buildkite-plugin#34 we introduced our own script to validate the Gradle Wrapper which uses the official documentation for its implementation. This PR uses that script to add a prerequisite step to validate the Gradle Wrapper in both pipelines.

The main reason we decided to add our own script as opposed to using the official Github Action was to be able to validate the Gradle Wrapper before running any of the Buildkite steps. As discussed in that PR, there are some edge cases our script doesn't cover. Furthermore, because it's a custom implementation, there is always a chance that it gets outdated. Therefore, we are adding the official Github Action alongside our own script.

After this PR is merged, I suggest we add the Github Action as a required step for trunk branch. The Buildkite step is already a prerequisite for the rest of the steps, so I don't think we need to add it as a required check, but having the Github Action as a required check should give us some extra peace of mind. Github only takes ~20s to validate the wrapper, so it shouldn't block developers unless there is an issue with it.

To Test
Verify that the Gradle Wrapper Validation is added as a prerequisite step to the Buildkite pipeline.

[ParaskP7]

👋 @oguzkocer !

Great work on the adding the Gradle Wrapper Validation checks in Simplenote Android! 🥇 ❤️ 🚀

I've reviewed and tested the PR as per the description and everything LGTM:

• Configuration Changes ✅
• Buildkite ✅
• GitHub Actions ✅

After this PR is merged, I suggest we add the Github Action as a required step for trunk branch.

I totally agree! 💯

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PS: I only have one question (❓) related to the extra notify configuration (see comment below). But, other than that I am approving the PR, I don't want to block it.