Community-maintained Capacitor package

[hyochan]

Continuing PR #589, which proposes a Capacitor wrapper over OpenIAP's native packages.

We're keeping this outside the official framework release train for now. The path discussed in the PR is a community-maintained package in its own repository, with iOS and Android example builds using the published OpenIAP packages.

@ingdas, thank you for the work. Let's continue here with any questions about publishing it independently. Once the package is published and those builds pass, we can link it from the docs as a community package that OpenIAP doesn't verify.