feat(smus): Upgrade sdk v2 to sdk v3 - SQLWorkbench

[PotatoWKY]

Summary

This PR migrates the SQLWorkbench custom API client from the deprecated AWS SDK v2 generator pattern to standalone AWS SDK v3-compatible packages. This migration is required as part of the broader AWS Toolkit repository migration from SDK v2 to v3.

Problem

The AWS Toolkit VSCode repository is deprecating the centralized generateServiceClient.ts script that generates TypeScript clients from service JSON definitions. The SageMaker Unified Studio (SMUS) team currently uses this v2 generator for SQLWorkbench.

Solution

• Created standalone package @amzn/sql-workbench-client
• Updated imports to use new standalone package
• Migrated from SDK v2 .promise() pattern to SDK v3 Command pattern (client.send(command))
• Updated credential handling to use credential provider function for auto-refresh support
• Replaced local type definitions with SDK-provided types (DatabaseConnectionConfiguration, ParentResource, Resource, etc.)
• Removed dependency for SQLWorkbench on the deprecated generateServiceClient.ts script
• Updated unit tests to mock SDK v3 send method instead of v2 .promise() pattern

---

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[github-actions]

• This pull request implements a feat or fix, so it must include a changelog entry (unless the fix is for an unreleased feature). Review the changelog guidelines.
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[liuzulin]

Can you describe what manual tests you performed for this change

[liuzulin]

Why we need this change? let's avoid default to empty unless it's necessary

[PotatoWKY]

Yeah this is needed.

SDK v3 Type Definitions:

From the new @amzn/sql-workbench-client SDK v3 (3.0.0.tgz):

// ParentResource interface - parentId is required string
export interface ParentResource {
    parentId: string;  // Required, non-nullable
    parentType: string;
}

// DatabaseConnectionConfiguration - database is optional
export interface DatabaseConnectionConfiguration {
    // ...
    database?: string | undefined;  // Optional
}

The Problem:

schemaConnectionConfig.database has type string | undefined (because database is optional in DatabaseConnectionConfiguration)
parentId in ParentResource requires type string (non-nullable)
TypeScript won't allow assigning string | undefined to string
The Fix:

parentId: schemaConnectionConfig.database || ''

[PotatoWKY]

Can you describe what manual tests you performed for this change

• Tested expanding every node under Data Explorer, compared to make sure it has the same behavior as the extension from marketplace
• Tested expanding half of the nodes under Data Explorer, waited ~25 mins, expand rest of the nodes