feat(fabric-server): create fabric-server package

pkgs/fabric-server/default.nix

@@ -0,0 +1,43 @@
+{ callPackage, writeTextFile, writeShellScriptBin, minecraft-server, jre_headless }:
+
+let
+  loader = callPackage ./generate-loader.nix { };
+  log4j = writeTextFile {
+    name = "log4j.xml";
+    text = ''
+      <?xml version="1.0" encoding="UTF-8"?>
+      <Configuration status="WARN" packages="com.mojang.util">
+          <Appenders>
+              <Console name="SysOut" target="SYSTEM_OUT">
+                  <PatternLayout pattern="[%d{HH:mm:ss}] [%t/%level]: %msg%n" />
+              </Console>
+              <Queue name="ServerGuiConsole">
+                  <PatternLayout pattern="[%d{HH:mm:ss} %level]: %msg%n" />
+              </Queue>
+              <RollingRandomAccessFile name="File" fileName="logs/latest.log" filePattern="logs/%d{yyyy-MM-dd}-%i.log.gz">
+                  <PatternLayout pattern="[%d{HH:mm:ss}] [%t/%level]: %msg%n" />
+                  <Policies>
+                      <TimeBasedTriggeringPolicy />
+                      <OnStartupTriggeringPolicy />
+                  </Policies>
+                  <DefaultRolloverStrategy max="1000"/>
+              </RollingRandomAccessFile>
+          </Appenders>
+          <Loggers>
+              <Root level="info">
+                  <filters>
+                      <MarkerFilter marker="NETWORK_PACKETS" onMatch="DENY" onMismatch="NEUTRAL" />
+                  </filters>
+                  <AppenderRef ref="SysOut"/>
+                  <AppenderRef ref="File"/>
+                  <AppenderRef ref="ServerGuiConsole"/>
+              </Root>
+          </Loggers>
+      </Configuration>
+    '';
+  };
+in
+# Taken from https://github.com/FabricMC/fabric-installer/issues/50#issuecomment-1013444858
+writeShellScriptBin "minecraft-server" ''
+  echo "serverJar=${minecraft-server}/lib/minecraft/server.jar" >> fabric-server-launcher.properties
+  exec ${jre_headless}/bin/java -Dlog4j.configurationFile=${log4j} $@ -jar ${loader} nogui''