The purpose of this commit is to return meaningful responses when
validating steps and leave the caller to decide what to do with them.
We also introduce a public action enabling the validation of a step
from its xmlid and handle the different cases including the missing
step.
Note: these features are currently used in appointment (See Ent PR).
Additionally, returning the newly validated `onboarding_steps` from
`onboarding_step.action_set_just_done` makes more sense than returning
the `onboarding_progress_steps` records.
Tests are updated to make sure of this.
Task-3074112
closesodoo/odoo#114572
Related: odoo/enterprise#37870
Signed-off-by: Warnon Aurélien (awa) <awa@odoo.com>