Add "Forgot password" to sign in screen

Multiple community posts have been made about forgotten passwords. There has since been added a [recovery mechanism ](https://docs.influxdata.com/influxdb/v2.1/reference/cli/influxd/recovery) but people aren't finding that easily. To scale this, it might be worth having the universally understood "Forgot password" button on the login screen. This button could simply point to these docs for now. We may want something more robust in the future but this could be good for now.

Locate the sign-in screen and its existing login controls, then read the linked recovery documentation to confirm the destination. Add a universally recognizable “Forgot password” entry that points to that recovery mechanism; done means users can reach the documented recovery flow from the login screen.

Written by the indexing model from the issue text.