Draft add vellum client guides

[koladev32]

Notes for reviewers and delivery:

• The Gram sections are reused from the Anthropic guide for the API client guide, and n8n for the Client guide. It means that the same assets can be used but it might need renaming.
• Here is the code example for the API client feat add vellum code example speakeasy-examples#20

[ritza-publishing-assistant]

https://github.com/ritza-co/speakeasy-developer-docs/blob/draft/add-vellum-client/docs/gram/api-clients/using-vellum-workflows-sdk-with-gram-mcp-servers.mdx (1191)
https://github.com/ritza-co/speakeasy-developer-docs/blob/draft/add-vellum-client/docs/gram/clients/using-vellum-agents-with-gram-mcp-servers.mdx (1179)

Total word count: 2370

[ritza-publishing-assistant]

28 image files optimized