gerd.postgresql: initial add

shared/applications/server/postgresql.nix

@@ -0,0 +1,31 @@
+{ config, ... }:
+
+{
+  services.postgresql = {
+    enable = true;
+  };
+
+  # backup postgresql databases (everything in ensuredatabases)
+  services.postgresqlBackup = {
+    enable = true;
+
+    compression = "zstd";
+
+    # default to backup all databadatabases
+    databases = config.services.postgresql.ensureDatabases;
+  };
+
+  # default the locale to C. I have NO CLUE why you would
+  # like to use any other locale, than the default C.
+  # However, matrix synapse complains A LOT if it isn't C,
+  # so we just default to it! No worries!
+  # Matrix Synapse Locale Note
+  #   - https://github.com/element-hq/synapse/blob/develop/docs/postgres.md#fixing-incorrect-collate-or-ctype
+  # NOTE from postgresql here https://www.postgresql.org/docs/current/locale.html
+  # Using C.UTF-8, because setting `LC_CTYPE=C` will default encoding to SQL_ASCII.
+  # https://pganalyze.com/blog/5mins-postgres-17-builtin-c-utf8-locale
+  systemd.services.postgresql.environment = {
+    LC_CTYPE = "C.UTF-8";
+    LC_COLLATE = "C";
+  };
+}