[lldb-vscode] Add missing launchCommands entry in the package.json

Summary:
https://reviews.llvm.org/D65363 introduced the launchCommands argument. However, it did not add
a corresponding definition in the package.json

Reviewers: clayborg, labath, kusmour, aadsm

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D76529