solitary: Add missing Synapse log configuration

nixos/config/solitary/log_config.yaml

@@ -0,0 +1,22 @@
+version: 1
+formatters:
+  journal_fmt:
+    format: '%(name)s: [%(request)s] %(message)s'
+
+filters:
+  context:
+    (): synapse.util.logcontext.LoggingContextFilter
+    request: ""
+
+handlers:
+  journal:
+    class: systemd.journal.JournalHandler
+    formatter: journal_fmt
+    filters: [context]
+    SYSLOG_IDENTIFIER: synapse
+
+root:
+  level: WARNING
+  handlers: [journal]
+
+disable_existing_loggers: False