feat(amazonq): added dev override for registry URL

[ashishrp-aws]

Problem

Developers need a way to override the MCP registry URL for testing and development purposes without modifying production code or waiting for backend profile configuration changes. Currently, the registry URL is only fetched from the getProfile API call, making it difficult to test against different registry endpoints during development.

Solution

Added a new developer setting aws.dev.amazonqRegistry with a registryUrl field that allows overriding the MCP registry URL from VSCode settings. The override takes precedence over the URL fetched from getProfile, enabling developers to easily test against custom registry endpoints.

Changes:

• VSCode Extension: Added amazonqRegistry to dev settings, extracted registryUrl from config, and passed it to the language server via initialization options
• Language Server: Added registryUrl to client capabilities, updated ProfileStatusMonitor to accept and prioritize override URL, and modified McpToolsServer to use the override when initializing MCP Manager

Usage:

{
    "aws.dev.amazonqRegistry": {
        "registryUrl": "https://custom-registry.example.com/manifest.json"
    }
}

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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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