docs: make cloud overview more descriptive

#### Current State
The content/en/cloud/overview/_index.md file currently serves as a generic Docsy template placeholder. It contains "under construction" alerts and a list of questions (e.g., "What is it?", "Why do I want it?") hidden within HTML comments, rather than providing actual information about Layer5 Cloud. This results in a poor user experience for individuals looking to understand the platform's core capabilities.

#### Desired State
The Cloud Overview page should provide a professional, high-level summary of Layer5 Cloud as the central management console for Kanvas and Meshery. It should explicitly define the platform's value proposition—such as collaborative infrastructure design and unified identity management—while removing all template-specific "placeholder" text and construction warnings to ensure the documentation is production-ready.

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#### Contributor Guide and Resources
- 📚 [Instructions for contributing to documentation](https://github.com/layer5io/docs/blob/master/CONTRIBUTING.md)
- Layer5 documentation [site](https://docs.layer5.io) and [source](https://github.com/layer5io/docs/)
- 🎨 Wireframes and [designs for Layer5 site](https://www.figma.com/file/5ZwEkSJwUPitURD59YHMEN/Layer5-Designs) in Figma [(open invite)](https://www.figma.com/team_invite/redeem/GvB8SudhEOoq3JOvoLaoMs)
- 🙋🏾🙋🏼 Questions: [Layer5 Discussion Forum](https://discuss.layer5.io) and [Layer5 Community Slack](http://slack.layer5.io)