config: refactor and replace structopt by clap

This greatly refactors and simplifies the config parsing.

Also, it removes the possiblity to specify user and password,
since this has been phased out by Spotify and will be replaced by OAuth.

Cargo.toml

@@ -18,12 +18,10 @@ fern = { version = "0.7.0", features = ["syslog-6"] }
 futures = "0.3.15"
 gethostname = "0.5.0"
 hex = "0.4"
-keyring = { version = "3.5", optional = true, features = ["apple-native", "windows-native", "sync-secret-service"] }
 libc = "0.2.82"
 log = "0.4.6"
 serde = { version = "1.0.115", features = ["derive"] }
 sha-1 = "0.10"
-structopt = "0.3.17"
 tokio = {version = "1.26.0", features = ["signal", "rt-multi-thread", "process", "io-std"] }
 tokio-stream = "0.1.7"
 url = "2.2.2"
@@ -39,6 +37,7 @@ color-eyre = "0.6"
 directories = "5.0.1"
 thiserror = "2.0"
 time = { version = "0.3.37", default-features = false, features = ["formatting"] }
+clap = { version = "4.5.23", features = ["derive"] }
 
 [target."cfg(unix)".dependencies]
 daemonize = "0.5"
@@ -55,7 +54,6 @@ env_logger = "0.11"
 
 [features]
 alsa_backend = ["librespot-playback/alsa-backend", "alsa"]
-dbus_keyring = ["keyring"]
 dbus_mpris = ["dbus", "dbus-tokio", "dbus-crossroads"]
 pipe_backend = []
 default = ["alsa_backend", "pipe_backend"]