Adding Gravity as contributors to Ossie

[drewgillson]

Summary

This PR adds Gravity to the Apache Ossie ecosystem page by including the Gravity logo and company name.

About Gravity's Ossie Contribution

Gravity builds Orion, an AI analyst that grounds its analysis in the business logic companies already keep in their semantic layers.

Current Ossie-related work includes:

• Adopting Apache Ossie as the interchange format for Orion's Metrics Catalog, so governed metric definitions move in and out in an open format.
• Mapping Ossie datasets, fields, relationships, metrics, and AI-context annotations onto Orion's existing catalog model.
• Building on the semantic extraction Orion already ships for LookML and dbt, with Ossie as the vendor-neutral intermediate representation.
• Grounding SQL generation in Ossie's AI-context annotations: instructions, synonyms, and example queries.
• Supporting interoperability so semantic definitions stay portable across BI and AI tools.

This addition reflects Gravity's adoption of Apache Ossie and its commitment to keeping semantic definitions portable rather than locked to one vendor.

Changes

• Added the Gravity logo to docs/assets/images/logos/, the directory the ecosystem template reads from.
• Added the Gravity company name to the Ossie ecosystem section in data/ecosystem.yml.

Testing

• Verified that the website builds successfully with the project's Docker image (mkdocs build).
• Verified that the logo renders correctly in the ecosystem grid, at a size consistent with neighbouring entries.
• Verified that the ecosystem page renders correctly.
• Verified that no existing contributors were removed.
• Verified that the new entry is positioned in alphabetical order, between GoodData and Hex.