Modify the Ewoks schema specification

The latest version of the Ewoks schema specification is held in the LATEST_VERSION variable in src/ewokscore/graph/schema/__init__.py.

When changing the Ewoks schema specification, this version should be changed depending on the change: - When adding a backward-compatible change (e.g. a new optional field), the minor part of the version should be incremented (e.g. go from 1.0 to 1.1) - When adding a breaking change (e.g. a new required field or a change in structure), the major part of the version should be incremented (e.g. go from 1.1 to 2.0).

Then, ewokscore version bounds for this schema version should be added: the lowest ewokscore version that supports this schema and the highest version that supports this schema.

For this, edit get_version_bounds by adding an entry to _VERSION_BOUNDS. Change the upper bound of the previous schema if needed.

—

Finally, an update method should be added to convert the previous schema version to the new version.

For example, say we updated the version to 2.0 from 1.1. Then, we need to add a Python module called v1_1 in src/ewokscore/graph/schema with a function update_graph_schema. This function should take care of converting a graph of schema version 1.1 to a graph of schema version 2.0. The content of this function depends on the change made to the schema.