Before this commit, the chart's dataSources were managed by the core plugin
`OdooChartCorePlugin`. This didn't make sense since dataSources aren't
core data:
- they are neither exported nor imported
- they can be different for each user (their ids were generated via uuidv4
at import)
Moved the dataSources management to the UI plugin `OdooChartUIPlugin` and moved
the relevant getters inside this plugin. Changed the ids of the dataSources
to be the same as the chart's id + a prefix, to avoid having to maintain a
mapping `chartId` <=> `dataSourceId` .
closesodoo/odoo#120136
Task: 3293491
Related: odoo/enterprise#40546
Signed-off-by: Lucas Lefèvre (lul) <lul@odoo.com>