feat: Unity Asset Store Integration

[bitsandfoxes]

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Releasing to the Unity Asset Store requires manual import of the package and upload through the Editor. This means we do have access to the actual source that is getting shipped and enables us to add

options.AddIntegration(new SentryUnityAssetStoreIntegration());

to the SentryIntegrations https://github.com/getsentry/sentry-unity/blob/6484482bfa9946d2514579eec0371003884e6f42/package-dev/Runtime/SentryIntegrations.cs#L18-L20 that is getting shipped with the package and compiled with the game.