Generate a versioned copy of the channel database when publishing #4470
Description
Desired behavior
Persist old versions of channel databases - in order to not make this onerous, we should do this in a forward looking way.
When a channel is published, continue the current behaviour of putting it in storage under the default name. Also put it into storage under the additional name:
<channel_id>-<channel_version>.sqlite3
This means that the next time the channel is published, we will still have a copy of this channel database.
Current behavior
When a channel is republished, the old channel database is overwritten and lost.
Value add
Prevent data loss, allow for inspecting historic channel versions for trouble shooting, allow for installation of historic channels, easier and repeatable testing of channel upgrade workflows.
Possible tradeoffs
This would add a small additional space requirement for a channel, that would grow over time. We might eventually want to place a limit on the number of historic versions if this became a concern.