Add pm-34171-card-scanner feature flag (#7477)

Introduced in 2026.4.1 Mobile releases (Android and iOS), enables use of
device camera to autofill a card type item.

N.B. This feature relies on Google ML Kit. F-Droid policy disallows
Google ML Kit. Because of this, F-Droid builds do not ship with card
scanner feature. (See https://github.com/bitwarden/android/pull/6890)

src/config.rs

@@ -1440,6 +1440,7 @@ pub const SUPPORTED_FEATURE_FLAGS: &[&str] = &[
     "mutual-tls",
     "cxp-import-mobile",
     "cxp-export-mobile",
+    "pm-34171-card-scanner",
     // Platform Team
     "pm-30529-webauthn-related-origins",
     // Vault Team