feat: add feature flag export-attachments

.env.template

@@ -357,6 +357,7 @@
 ## - "anon-addy-self-host-alias": Enable configuring self-hosted Anon Addy alias generator. (Needs Android >=2025.2.0)
 ## - "simple-login-self-host-alias": Enable configuring self-hosted Simple Login alias generator. (Needs Android >=2025.2.0)
 ## - "mutual-tls": Enable the use of mutual TLS on Android (Client >= 2025.2.0)
+## - "export-attachments": Enable support for exporting attachments (Clients >=2025.4.0)
 # EXPERIMENTAL_CLIENT_FEATURE_FLAGS=fido2-vault-credentials
 
 ## Require new device emails. When a user logs in an email is required to be sent.

src/config.rs

@@ -846,6 +846,7 @@ fn validate_config(cfg: &ConfigItems) -> Result<(), Error> {
         "anon-addy-self-host-alias",
         "simple-login-self-host-alias",
         "mutual-tls",
+        "export-attachments",
     ];
     let configured_flags = parse_experimental_client_feature_flags(&cfg.experimental_client_feature_flags);
     let invalid_flags: Vec<_> = configured_flags.keys().filter(|flag| !KNOWN_FLAGS.contains(&flag.as_str())).collect();