Refine App Registry Structure & Schema

[salmad3]

Context:

As we iterate on the registry's initial version, we aim to refine the structure and organization of the app schema files to enhance maintainability and usability.

Follows #65 and @jeronimoalbi's suggestion in particular.

Acceptance Criteria:

• Directory Structure: Avoid using separate folders for each app schema unless necessary for additional content like images or documents. Propose storing all schemas at the same level within a renamed directory, enhancing file management and access.
• File Naming and Formats: Standardize the naming of schema files using a format such as foo_name.app.json. Consider the flexibility of supporting both JSON and YAML formats to accommodate different developer preferences.
• Registry and Schema Files: Transition from schema.app.json to registry.json to clarify its role as the main registry file, with individual app schemas using the .app.json suffix. Additionally, define a straightforward JSON schema (schema.json) to validate the app schemas.
• Folder Naming: Rename _ignite-app-registry to registry, simplifying the URL to https://github.com/ignite/apps/registry and improving semantic clarity.
• Schema Simplicity and Evolution: Maintain a simple schema initially, incorporating only necessary features. Expand the schema dynamically based on real-world use and developer feedback.

Notes:

• Look to established standards like package.json and pyproject.toml for best practices in schema design.
• For defining the schema validation, refer to the JSON Schema official documentation.

[jeronimoalbi]

If it helps, here's a schema.json and an example foo.app.json App schema to test it using for example https://www.jsonschemavalidator.net. Maybe it helps as an starting point for the final JSON schema.
It was defined at some point during app registry discussions so it might be a bit outdated.

[julienrbrt]

Closed by #95