Complete git history of plugins is missing about buildstream-plugins

[gtristan]

The history of plugins which were added to this new repo is still available in the respective repositories from whence they came, I don't think this is a problem.

I should also point out that there is not much significant history in buildstream-plugins that comes from bst-plugins-experimental, as listed out in https://gitlab.com/BuildStream/bst-plugins-experimental/-/issues/47, there is the cargo source which actually contains code, and the remaining promoted plugins are just BuildElement implementations (which means the history only really pertains to default .yaml files).

The remaining bulk of plugins in buildstream-plugins comes from buildstream itself (plus the docker source which comes from bst-plugins-container).

[jjardon]

Cool, I think a good compromise would be to document somwhere the origin of the plugins in case someone need to check the history