Add Prefect and Omni connectors

[jpnguyen]

Summary

Adds two new 2.0 connectors to the integrations list on open-metadata.org.

What changed

• Prefect in the Pipeline category (alongside Airflow, Dagster, Fivetran). Note: flagged as 'Integration' in the request, but the connectors taxonomy has no Integration category and Prefect is a workflow orchestrator, so it belongs in Pipeline (its docs live under /connectors/pipeline/).
• Omni in the Dashboard category (alongside Superset, Tableau, Power BI).
• Both link to the connectors index (https://docs.open-metadata.org/latest/connectors) since the per-connector docs pages are not live yet.
• Logos added to public/assets/services/ (prefect.webp, omni.webp), trimmed and sized to match existing connector logos.

Test plan

• Netlify preview: Prefect appears under Pipeline, Omni under Dashboard, logos render at the right size
• Links open the connectors index

🤖 Generated with Claude Code

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[jpnguyen]

@sweta1308