[bug]: installation/initial startup should not prompt to download ckpts that user already has

[damian0815]

configure_invokeai.py is always run during binary installation, and it always prompts user to download SD checkpoints. Optionally, it should check if models.yaml already exists and points to a valid ckpt; if so, the Download <r>ecommended models, <c>ustomize the list, or <s>kip this step? [r]: prompt should not appear, and the configure script should assume user wants to <s>kip. (perhaps this can be a command line arg that the installer uses).