Add max-player-auto-save-per-tick setting to spread out saves more

This will force the saves to spread over multiple ticks even when many
players auto save interval is aligned, avoiding spikes on large servers.

Closes #1021

Spigot-Server-Patches/Enforce-Sync-Player-Saves.patch

@@ -7,7 +7,7 @@ Saving players async is extremely dangerous. This will force it to main
 the same way we handle async chunk loads.
 
 diff --git a/src/main/java/net/minecraft/server/PlayerList.java b/src/main/java/net/minecraft/server/PlayerList.java
-index 0e82c16b7..4080ed26c 100644
+index efea22c92..91136a8d8 100644
 --- a/src/main/java/net/minecraft/server/PlayerList.java
 +++ b/src/main/java/net/minecraft/server/PlayerList.java
 @@ -0,0 +0,0 @@ public abstract class PlayerList {
@@ -17,7 +17,7 @@ index 0e82c16b7..4080ed26c 100644
 +        MCUtil.ensureMain("Save Players", () -> { // Paper - ensure main
          long now = MinecraftServer.currentTick;
          MinecraftTimings.savePlayers.startTiming(); // Paper
-         for (int i = 0; i < this.players.size(); ++i) {
+         int numSaved = 0; // Paper
 @@ -0,0 +0,0 @@ public abstract class PlayerList {
              }
          }