[Feature Request] Make app validation optional when using pages

[AnnMarieW]

When using pages to make a multi page app, one of the nice features is that it automatically validates the layout. However as pointed out in this forum post it can make the initial load of an app slow if some of the layout functions are slow.

A possible solution is to make the validation optional, then this section would be skipped. (I tried it and it seems to work)

Validation could be turned off like this:

app = das.Dash(__name__, use_pages=True, set_validation_layout=False,  suppress_callback_exceptions=True)

or maybe if set_validation_layout=False, it could automatically set suppress_callback_exceptions=True

Any downside to doing this?