MCUs Deploy Step does not automatically update

While working on https://bugreports.qt.io/browse/QDS-13763 I've noticed a major problem with how MCU deploy step is set. 

AFAIU the MCU Build Step is:

• created when project is created/opened
• only if the step was not defined before.

That means that when a user modifies the .qmlproject it does not get updated. That also means that if someone had a project created with an old version of QDS (without the changes in 13763) then their deploy step will also not be updated.

This seems like an oversight from UX perspective. Perhaps some watcher on .qmlproject could help with that. Moreover, it seems that `DeployMcuProcessStep` is being rebuilt each time and current API does not allow for updating just the include dirs which would be inefficient.