[csolution-rpc] Add ListMissingPacks method

[brondani]

Fixes

• Relates to [csolution rpc] Add methods for discovering layers and listing missing packs cmsis-toolbox#419

Changes

Checklist

• 🤖 This change is covered by unit tests (if applicable).
• 🤹 Manual testing has been performed (if necessary).
• 🛡️ Security impacts have been considered (if relevant).
• 📖 Documentation updates are complete (if required).
• 🧠 Third-party dependencies and TPIP updated (if required).