Add PV UUID

[peterdudfield]

Add UUID to PV system table this can be optional feed.

This will allow the same uuid to be entered from the new pv-site database. This will allow us to deploy a ML model that reads the current pv database but saves stuff to the new pv-site database.

Then we can copy the UUIDs from the new database over to this

this is a bit of a hack, but not too much effort. This will be sorted when we do https://github.com/openclimatefix/PVConsumer/issues/46 and https://github.com/openclimatefix/ocf_datapipes/issues/144

[peterdudfield]

@devsjc do we want to do this as a bit of paired session to show you how alembic works. tasks are

• add new column
• make migrations
• apply migrations

[peterdudfield]

Actually hold fire on this. we could just allow the write function to pass id's insterad of uuids. This would keep te originla database neater. Ill add a n issue for that

[peterdudfield]

Dont need this any more, decided to save to the new database