feat(oauth2): handle refresh token expiration

Refresh tokens can expire after a certain amount of time. The expiration can happen during a live session or when the Toolbox is closed.
Inspecting the coder code it looks like 400 Bad request is raised
```
{
"error": "invalid_grant",
"error_description": "The refresh token is invalid or expired"
}
```

when we try to refresh an access token with an expired refresh token. Coder Toolbox should be able to handle this scenario.