Channels last support

Add --gradio-auth command line argument to enable Gradio authentication

Allows you to pass in Gradio authentication like:
`--auth username:password`
Supports multiple sets of credentials by comma-delimiting, like:
`--auth user1:pass1,user2:pass3`...

Add --hide-ui-dir-config command line flag

changed default cfg_scale to a higher value

Adds a "samples filename format" option in the settings. This format can be defined by tags for maximum flexibility and scalability.

Adds `--hide-ui-dir-config` flag to disable editing directory configs from the web UI. This can be set to prevent users from setting the directory to somewhere they shouldn't, for public (or semi-public) interfaces.

Directories are still read from config.json, so the server admin can still set them in the web UI and then relaunch with the hide flag, or edit the config manually.

Also:
- fix OptionInfo `component_args` keyword argument not being read if `component` isn't also set
- ensure that hidden settings aren't still read from the web UI (otherwise they could still be changed by tampering with the interface)