Implement SEP-1034: Default Values for Elicitation Schemas

[felixweinberger]

This is a tracking issue for implementation of SEP-1034.

Summary

This SEP extends the elicitation feature by adding support for default values across all primitive schema types (StringSchema, NumberSchema, and EnumSchema). The TypeScript SDK needs to implement the optional default field for these schema types, ensuring clients can pre-populate elicitation forms with reasonable default values to improve user experience and reduce manual input requirements. The feature must remain backward compatible as the default field is optional.

Related Issues & PRs

• Implementation PRs: n/a
• Related PRs: n/a
• Related Issues: n/a

[KKonstantinov]

Could take this one on if not assigned to anyone else.