Merge: nixos/matrix-synapse: configure PYTHONMALLOC when using jemalloc (#369444)

nixos/doc/manual/release-notes/rl-2505.section.md

···
 
 - `services.avahi.ipv6` now defaults to true.
 
+- For matrix homeserver Synapse we are now following the upstream recommendation to enable jemalloc as the memory allocator by default.
+
 - `bind.cacheNetworks` now only controls access for recursive queries, where it previously controlled access for all queries.
 
 - Caddy can now be built with plugins by using `caddy.withPlugins`, a `passthru` function that accepts an attribute set as a parameter. The `plugins` argument represents a list of Caddy plugins, with each Caddy plugin being a versioned module. The `hash` argument represents the `vendorHash` of the resulting Caddy source code with the plugins added.

nixos/modules/services/matrix/synapse.nix

···
 
         withJemalloc = mkOption {
           type = types.bool;
-          default = false;
+          default = true;
           description = ''
             Whether to preload jemalloc to reduce memory fragmentation and overall usage.
           '';
···
         baseServiceConfig = {
           environment = optionalAttrs (cfg.withJemalloc) {
             LD_PRELOAD = "${pkgs.jemalloc}/lib/libjemalloc.so";
+            PYTHONMALLOC = "malloc";
           };
           serviceConfig = {
             Type = "notify";