Use a prebuilt image

[josephjclark]

Rather than install the CLI each time the sync action runs, we should build a container with the CLI preinstalled.

We can use tags on dockerhub eg @stable @latest to control which image is used and ensure that the CLI version syncs with the latest lightning version

[josephjclark]

Bump node version at the same time

[josephjclark]

The aim is to have on action which always pull the latest versions of software