Allow using NTFY with access tokens

[Steltek]

Is your feature request related to a problem? Please describe.
NTFY supports authenticating via Basic auth with a username and password, or using access tokens. The latter can be used using an Authorization Bearer <tokenhere> header in the HTTP POST request, or using Basic Auth by simply submitting an empty username and the token as a password.

When entering the access token into the password, the authorisation appears to fail (I'm assuming speedtest-tracker doesn't try to do auth unless the username field is also filled in?).

Describe the solution you'd like
It would be nice if filling in just the password would cause speed-test tracker to submit an empty username and the password to NTFY to allow authenticating with tokens. (Even better if there was a separate field that used the 'bearer' method, but just having the empty username + password functionality would make it work.)

Additional context
NTFY documentation on using Access Tokens: https://docs.ntfy.sh/publish/#access-tokens