feat: add tokenLimits to model interface (#721)

## Problem
We need `maxInputTokens` field (used for dynamically calculating max
characters, generate assistant response input limit, etc)

## Solution
Add `maxInputTokens` field

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## License

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

Author: chungjac

types/chat.ts

@@ -724,10 +724,16 @@ export interface PromptInputOptionChangeParams {
     eventId?: string
 }
 
+export interface TokenLimits {
+    maxInputTokens?: number
+    maxOutputTokens?: number
+}
+
 export interface Model {
     id: string
     name: string
     description?: string
+    tokenLimits?: TokenLimits
 }
 
 export interface ListAvailableModelsParams {