add support for simple username/password login for parsers

[AwkwardPeak7]

Describe your suggested feature

currently MangaParserAuthProvider uses webview to login to a source. but there are sources which don't have a dedicated webpage for login or it doesn't work with the api to be used in the parser. So it either requires HTTP Basic auth on every request or a one time login request to get a token. Both cases require the app to support inputting username and password so parser can do appropriate authentication.

Acknowledgements

• This is not a duplicate of an existing issue. Please look through the list of open issues before creating a new one.