Gradio Auth Read from External File

Usage: `--gradio-auth-path {PATH}`
It adds the credentials to the already existing `--gradio-auth` credentials. It can also handle line breaks.
The file should look like:
`{u1}:{p1},{u2}:{p2}`
or
```
{u1}:{p1},
{u2}:{p2}
```
Will gradio handle duplicate credentials if it happens?