feat: add AI-generated branch names configuration and integration in Copilot CLI

[DonJayamanne]

No description provided.

[Copilot]

Pull request overview

Adds a new configuration flag to control whether Copilot CLI generates AI-based git branch names, and wires that flag into Copilot CLI session initialization so branch name generation can be disabled by default.

Changes:

• Introduced a new configuration key (chat.cli.aiGenerateBranchNames.enabled) and surfaced it in the extension’s package.json contributions + localized description.
• Gated GitBranchNameGenerator instantiation behind the new config flag when registering Copilot CLI services.
• Updated the Copilot CLI chat session participant to tolerate the branch name generator being absent.

Show a summary per file

File	Description
src/platform/configuration/common/configurationService.ts	Registers the new config key in ConfigKey.Advanced.
src/extension/chatSessions/vscode-node/chatSessions.ts	Reads the new config and conditionally creates GitBranchNameGenerator.
src/extension/chatSessions/vscode-node/copilotCLIChatSessions.ts	Makes branch name generation conditional on generator presence.
package.nls.json	Adds localized description string for the new setting.
package.json	Contributes the new setting (github.copilot.chat.cli.aiGenerateBranchNames.enabled) to VS Code configuration.

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 2