Add support for reauth flow

[functionpointer]

With #298 merged, we should also add support for the reauthentication flow.

This PR also simplifies exception management on initial poll, by using HA's built-in async_config_entry_first_refresh() function.
It will automatically raise ConfigEntryNotReady when an error occurs. This allows us to remove a big try: block.

[EdLeckert]

Seems to work fine. The result reason displayed in the dialog by async_abort seems a little rough, but I see that it is fairly common practice to do it this way.

Another thing I noticed that has probably been this way for a while is that a non-existent URL does not trigger an InvalidURL exception. Instead, it results in a timeout that displays as Unexpected error. Might want to look into that at some point.

[vinteo]

the rough message seems to be due to missing strings in the localisation? example:

https://github.com/home-assistant/core/blob/4fd92c17f077bf842d054a48c2af6ecc48722b74/homeassistant/components/androidtv_remote/strings.json#L35

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[vinteo]

thanks again