Add workflow to ensure generated code is up to date

[Xtansia]

Description

Add workflow to ensure generated code is up to date

Example of failing run: https://github.com/opensearch-project/opensearch-java/actions/runs/9736512856/job/26867247859?pr=1061

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[dblock]

This means that anyone contributing to the client will have to re-run the generator. So, if I am fixing an unrelated bug, I still will get a failure here. In that case, does an automatic workflow that runs on a cron to generate a PR update like opensearch-project/opensearch-py#767 make more sense?

[Xtansia]

This means that anyone contributing to the client will have to re-run the generator. So, if I am fixing an unrelated bug, I still will get a failure here. In that case, does an automatic workflow that runs on a cron to generate a PR update like opensearch-project/opensearch-py#767 make more sense?

The generator has a local copy of the spec checked into the repo (and doesn't yet have a auto-download mechanism), so this will always run against that copy, meaning it'll only detect changes if the spec or generator logic has been changed. I'm going to add a cron job later for auto-fetching & updating.