k/quotas: disable produce quota by default

* Reinterpret the 0 value of `target_quota_byte_rate` as disable (this
  is safe as previously the minimum value was 1MB, so noone has this set
  to 0)
* Change the default value to be disabled

src/v/config/configuration.cc

@@ -496,12 +496,13 @@ configuration::configuration()
   , target_quota_byte_rate(
       *this,
       "target_quota_byte_rate",
-      "Target request size quota byte rate (bytes per second) - 2GB default",
+      "Target request size quota byte rate (bytes per second) - disabled "
+      "default (= 0)",
       {.needs_restart = needs_restart::no,
        .example = "1073741824",
        .visibility = visibility::user},
-      2_GiB,
-      {.min = 1_MiB})
+      target_produce_quota_byte_rate_default,
+      {.min = 0})
   , target_fetch_quota_byte_rate(
       *this,
       "target_fetch_quota_byte_rate",

src/v/config/configuration.h

@@ -46,6 +46,9 @@ namespace config {
 /// can not depend on any other module to prevent cyclic dependencies.
 
 struct configuration final : public config_store {
+    constexpr static auto target_produce_quota_byte_rate_default
+      = 0; // disabled
+
     // WAL
     bounded_property<uint64_t> log_segment_size;
     property<std::optional<uint64_t>> log_segment_size_min;

src/v/kafka/server/client_quota_translator.cc

@@ -16,6 +16,8 @@
 
 #include <seastar/util/variant_utils.hh>
 
+#include <optional>
+
 namespace kafka {
 
 using cluster::client_quota::entity_key;
@@ -274,8 +276,11 @@ client_quota_translator::get_quota_config(client_quota_type qt) const {
 std::optional<uint64_t>
 client_quota_translator::get_default_config(client_quota_type qt) const {
     switch (qt) {
-    case kafka::client_quota_type::produce_quota:
-        return _default_target_produce_tp_rate();
+    case kafka::client_quota_type::produce_quota: {
+        auto produce_quota = _default_target_produce_tp_rate();
+        return (produce_quota > 0) ? std::make_optional<uint64_t>(produce_quota)
+                                   : std::nullopt;
+    }
     case kafka::client_quota_type::fetch_quota:
         return _default_target_fetch_tp_rate();
     case kafka::client_quota_type::partition_mutation_quota:

src/v/kafka/server/tests/client_quota_translator_test.cc

@@ -87,7 +87,7 @@ SEASTAR_THREAD_TEST_CASE(quota_translator_default_test) {
     fixture f;
 
     auto default_limits = client_quota_limits{
-      .produce_limit = scale_to_smp_count(2147483648),
+      .produce_limit = std::nullopt,
       .fetch_limit = std::nullopt,
       .partition_mutation_limit = std::nullopt,
     };