fix(cli): prevent empty sessions from being saved (#11076)

* add /sessions slash command

* do not save empty sessions

* update tests

* Update extensions/cli/src/services/ChatHistoryService.ts

Co-authored-by: cubic-dev-ai[bot] <191113872+cubic-dev-ai[bot]@users.noreply.github.com>

* remove duplicate telemetry capture

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Co-authored-by: cubic-dev-ai[bot] <191113872+cubic-dev-ai[bot]@users.noreply.github.com>