swarm-authelia: run the secret publisher and a journal forwarder inside the container

swarm-secret-publish and its path unit now run inside authelia's container,
beside the mint, and read each client secret at the path authelia writes it.
The host unit and host path unit, which read the secrets through the
container's root on the host, are gone, and so is
deploy.authelia.hostClientSecretDir, which only they read. The publisher keeps
its store identity, the secret-publisher leaf. The host hands the leaf and the
store's CA into the container as nspawn system credentials, and the unit loads
them; where this host mints the leaf, the container waits for swarm-bao-pki.
Authelia does not wait for the publisher, which retries every 30 seconds while
the store is down.

The container also runs the journal forwarder the other service containers
run, pushing to a receiver of its own on the swarm collector (serviceProducers
swarm-authelia) as a new machine OIDC client (swarm.authelia.otel.clientId)
that authelia registers for itself and the publisher carries to the store. The
fetch unit reads it back under the publisher's leaf, also handed to it as a
system credential, so the swarm-secret-publisher policy gains read on that one
leaf; its stanza keeps create and update, which the exact path would otherwise
take from the services/* prefix. Without the leaf the forwarder is off.

The container drops --link-journal=host, and the host collector stops reading
it. The services' "nothing at <path>" errors name the publisher in authelia's
container.

swarm-nats-auth/src/oidc_secret.rs

@@ -2,8 +2,8 @@
 //! with. Read from the secret store as the responder starts and held in
 //! memory, never in a file, `argv` or the environment.
 //!
-//! The secret can change under a running responder: authelia's host
-//! re-publishes it when it is re-minted. So when the `IdP` refuses an
+//! The secret can change under a running responder: the publisher in authelia's
+//! container re-publishes it when it is re-minted. So when the `IdP` refuses an
 //! introspection as a credential (a 400 or 401), the secret is read from the
 //! store again ([`StoredSecret::after_refusal`]) and, when it changed, the
 //! introspection is tried once more. Both fit in the one request's
@@ -43,7 +43,9 @@ pub fn path(client_id: &str) -> Result<String> {
 /// When the store cannot be read, or holds nothing or only whitespace there.
 pub async fn read(store: &impl KeyStore, path: &str) -> Result<String> {
     let stored = store.read(path).await?.with_context(|| {
-        format!("nothing is stored at {path}; swarm-secret-publish on authelia's host writes it")
+        format!(
+            "nothing is stored at {path}; swarm-secret-publish in authelia's container writes it"
+        )
     })?;
     let trimmed = stored.trim();
     if trimmed.is_empty() {