Add nightly playground

[gaiksaya]

Description

This change adds the initial draft of nightly playgrounds with below specifics:

1. distribution version, distribution urls are grabbed on the go whereas all other important parameters are hardcoded in the code
2. Adds tests
3. Adds GHA workflow to run tests

Issues Resolved

#129

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[peterzhuamazon]

So from the looks of it, this is basically import cluster cdk, and deploy a stack of OpenSearch / Dashboards with provided url?

Just wondering why cant we use the existing cluster cdk directly?

Thanks.

[peterzhuamazon]

Think pr trigger is enough here.

[gaiksaya]

So from the looks of it, this is basically import cluster cdk, and deploy a stack of OpenSearch / Dashboards with provided url?

Just wondering why cant we use the existing cluster cdk directly?

Thanks.

The reason we went with this approach is to reduce the context variables and source code what is required for this use case. Such as security should always be enabled. Also, for future stacks, we can extend / depend on this base stacks. Another reason was to stick to 1 version of opensearch-cluster-cdk. The project is pretty new and has active changes coming in more often which we need not be bothered unless required.

[peterzhuamazon]

@gaiksaya confirms that mend error is not related.
Approved now, thanks.