Improve setup documentation, sample artifacts, and Redis/TLS configuration

[Shamly-Shanawaz]

Purpose

This PR introduces the following changes:

• Reworked README.md to provide clearer prerequisites, config file setup, DB creation steps, and notes on handling TLS / self-signed certificate errors.
• Added new sample API content for CountriesAPI and LeisureActivitiesAPI, plus updated/added artifact scripts to seed org, API, and theme data.
• Updated Redis connection helper/service and sample_config.json to better reflect current Redis/TLS configuration options.
• Removed the legacy docs/InstallationGuide.md now that the main README covers installation and local setup.

Issues

https://github.com/wso2-enterprise/apim-saas/issues/1604

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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