[formrecognizer] Address Arch Board Feedback

[kristapratico]

• follow up if there could be something labeled that is not text when thinking of naming for FieldText. Should this be FieldData or alternate naming? Otherwise property/model naming difference between languages is okay Tracked in [formrecognizer] more renames to allow for non-text elements #12274
• requested_on and completed_on should be renamed to training_started_on and training_completed_on [formrecognizer] arch board feedback renames #12207
• possibly add training duration - need to understand if this is something users want/need Tracked in [formrecognizer] Consider adding a training duration #12277
• need to make sure we do support local file paths for containers Tracked in [formrecognizer] support container local file paths #12276
• KC doesn't like submodels - should we brainstorm naming for the property/model here some more? Feature team decided "No".
• KC didn't like CustomFormModel and preferred this to be something like TrainingResult Feature team decided "No".

[kristapratico]

Spun off anything pending into new issue, closing this