Add HTTP Basic Auth

All write endpoints and the manage
routes are gated behind HTTP Basic Auth middleware; credentials are
configured via [auth] in config.toml or APP__AUTH__USERNAME /
APP__AUTH__PASSWORD environment variables.

Cargo.toml

@@ -22,3 +22,4 @@ thiserror = "1"
 mime_guess = "2"
 tokio-util = { version = "0.7", features = ["io"] }
 bytes = "1"
+base64 = "0.22"