Merge upstream v0.16.23

Five conflicts, resolved:

- crates/common/src/auth/authentication.rs: upstream's get_directory_for_token
  and JwtClaims replace extract_jwt_domain; the per-domain directory code
  (DIR-1, DIR-5 to DIR-7) is kept, and the token lookup routes through it.
  The release's one new Enterprise snippet was the body of
  get_directory_for_issuer, which stays returning None: a token naming no
  address gets the server default, as DIR-2 specifies and as v0.16.22 did.
- crates/common/src/manager/application.rs: upstream's rewrite of the tests,
  with the temp directory names renamed again, and the 5(a) notice the
  name-purge change should have added.
- crates/common/src/network/mta.rs: both sides' imports.
- crates/main/Cargo.toml: the AGPL-only license kept, version 0.16.23.
- Cargo.lock: upstream's, with the fork's crates added by Cargo.

crates/services/src/task_manager/mod.rs

@@ -137,4 +137,20 @@ impl TaskResult {
             max_attempts: None,
         }
     }
+
+    pub fn deferred(retry_at: Option<u64>, message: impl Into<String>) -> Self {
+        match retry_at {
+            Some(retry_at) => TaskResult::Failure {
+                typ: TaskFailureType::Retry(retry_at),
+                message: message.into(),
+                max_attempts: None,
+            },
+            None => TaskResult::temporary(message),
+        }
+    }
+}
+
+pub(crate) fn deferred_retry_time(err: &trc::Error) -> Option<u64> {
+    err.value(trc::Key::NextRetry)
+        .and_then(|value| value.to_uint())
 }