Added new section for third-party mcp access

[hterminasyan]

What reference architecture does this PR apply to?

outlines the two predominant patterns for third-party MCP access, the governance guardrails each pattern requires, and SAP's recommended approach for production-grade agentic access to SAP solutions.

Who should review your contribution? (Use @mention)

@kay-schmitteckert @anirban-sap @mschfer

Checklist before submitting

• My commits are only for the reference architecture mentioned above.
• I have followed the folder structure in the main README

[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
2 out of 4 committers have signed the CLA.

✅ navyakhurana
✅ hterminasyan
❌ Ter-Minasyan
❌ mschfer

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[kay-schmitteckert]

Looks good to me in general, some remarks:

• SAP BTP instead of BTP only + introduce SAP Business Technology Platform (BTP)
• SAP Cloud Identity Services (IAS) => (CIS) not (IAS) + Link to SAP Help: https://help.sap.com/docs/cloud-identity-services
• introduce IAS
• animation flow direction of the drawio diagram seems to be messed up

[navyakhurana]

Hi @hterminasyan, thank you for your contribution.
Can you also sign the CLA as well?

[navyakhurana]

Hi @hterminasyan is it good to go from your side?
As I see Anirban marked this PR as ready for review.

Regards,
Navya