Generate a versioned copy of the channel database when publishing

[rtibbles]

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.

[poju3185]

@rtibbles Could you review my PR? Thanks.

[rtibbles]

I have assigned you - and will have a look. Please ask to be assigned for any future issues like you did elsewhere!

[poju3185]

Understood, thank you for letting me know!