feat(patterns): add Gateway Pattern for multi-platform MCP aggregation

[keewillidevnet]

Add the Gateway Pattern to agentic_patterns, describing an architectural approach for aggregating multiple MCP servers behind a single entry point using AGNTCY components (Agent Directory, OASF, Identity, TBAC, SLIM, Observability).

Includes centralized, edge-native, and hybrid topology variants with support for Cisco IOx, Dell TPCM/SONiC, and whitebox switches. Defines seven agent types that compose multi-platform workflows through the gateway. References MIGA MCP Gateway as a reference implementation.

Follows up on agntcy/docs#392 per maintainer feedback to place pattern documentation in coffeeAGNTCY/agentic_patterns.

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Type of Change

• Bugfix
• [X ] New Feature
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• [X ] Documentation
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• [X ] I have read the contributing guidelines
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• [X ] Functionality is documented
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[keewillidevnet]

@jparello following up on agntcy/docs#392 — I moved the Gateway Pattern into agentic_patterns here as you suggested, and just pushed an update tightening the reference-implementation section so it matches the current MIGA repo. It's passing checks and cleanly mergeable against agentic-patterns. The doc covers centralized, edge-native (on-device MCP via IOx, Dell TPCM/SONiC, whitebox SONiC), and hybrid topologies. Whenever you or the team have a chance to review, I'd appreciate it. And per your note about bringing patterns into the demonstrations, I'm glad to contribute more and help wire these into coffeeAGNTCY whenever you want to start.