[WIP] Add command palette option to work on issue by number

[Copilot]

• Add new command issue.startWorkingByNumber to package.json commands list
• Add command palette entry for issue.startWorkingByNumber (without "when": "false")
• Register command implementation in issueFeatureRegistrar.ts to prompt for issue number
• Add localization string for the new command
• Test the new command manually to ensure it works

Original prompt

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This section details on the original issue you should resolve

<issue_title>"Start working on issue" should appear in command palette</issue_title>
<issue_description>Similar to the command that lets me open a PR by number, I want to say "Work on issue" -> enter the issue #, rather than find it in a query in the vscode view, because I will usually start in my github.com notifications</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes "Start working on issue" should appear in command palette #3529

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