We need to fetch undelivered messages from the database by the receiver which is `toDeviceID` field in our case.
`findMessageItemsByReceiever` method was implemented for this purpose.
Related linear task: [[ https://linear.app/comm/issue/ENG-510/document-services-vscode-dev-environment | ENG-751 ]]
[[ https://www.notion.so/commapp/Tunnelbroker-aae84e17d9834a6b97e9510f466e20f5 | Architecture review ]] for the tunnelbroker.