Default to no http read timeout (#27879)

Elasticsearch offers a number of http requests that can take a while to
execute. In #27713 we introduced an http read timeout that defaulted to
30 seconds. This means that if no reads happened for 30 seconds (even
after a request is received), the connection would be closed due to
timeout.

This commit disables the read timeout by default to allow us to evaluate
the impact of read timeouts and to avoid introducing distruptive
behavior.

Author: Tim-Brooks

core/src/main/java/org/elasticsearch/http/HttpTransportSettings.java

@@ -95,8 +95,9 @@ public final class HttpTransportSettings {
     public static final Setting<Boolean> SETTING_HTTP_RESET_COOKIES =
         Setting.boolSetting("http.reset_cookies", false, Property.NodeScope);
 
+    // A default of 0 means that by default there is no read timeout
     public static final Setting<TimeValue> SETTING_HTTP_READ_TIMEOUT =
-        Setting.timeSetting("http.read_timeout", new TimeValue(30, TimeUnit.SECONDS), new TimeValue(0), Property.NodeScope);
+        Setting.timeSetting("http.read_timeout", new TimeValue(0), new TimeValue(0), Property.NodeScope);
 
     public static final Setting<Boolean> SETTING_HTTP_TCP_NO_DELAY =
         boolSetting("http.tcp_no_delay", NetworkService.TCP_NO_DELAY, Setting.Property.NodeScope);