ZOOKEEPER-4741: Modernize PrometheusMetricsProvider with Jetty and new client

In production environments under heavy load, the existing
PrometheusMetricsProvider can introduce high latency. This is largely
due to its use of the outdated `io.prometheus.client` (simpleclient 0.x)
library and its basic, built-in HTTPServer, which has limitations in
server configuration and threading.

This commit modernizes the entire component to address these
performance and maintainability issues by:

1.  **Upgrading to the `io.prometheus.metrics` (client_java 1.x) library.**
    This aligns the provider with the current standard for Prometheus
    instrumentation in Java and ensures future compatibility.

2.  **Replacing the legacy server and threading model with an embedded
    Jetty server.** The previous implementation used a custom thread
    pool for a metrics processing task queue, which is now obsolete in
    the new client library. This has been replaced with a robust Jetty
    server, which uses its own configurable thread pool to handle
    exporter servlet requests directly. This change improves stability
    and simplifies the threading model, resolving the latency issues
    under load.

These changes make the PrometheusMetricsProvider more stable,
performant, maintainable, and easier to configure for production use.

Author: dukelion

zookeeper-metrics-providers/zookeeper-prometheus-metrics/pom.xml

@@ -23,7 +23,7 @@
   <parent>
     <groupId>org.apache.zookeeper</groupId>
     <artifactId>zookeeper-metrics-providers</artifactId>
-    <version>3.10.0-SNAPSHOT</version>
+    <version>3.8.4</version>
   </parent>
 
   <artifactId>zookeeper-prometheus-metrics</artifactId>
@@ -32,7 +32,8 @@
   <description>ZooKeeper Prometheus.io Metrics Provider implementation</description>
 
   <properties>
-      <prometheus.version>0.9.0</prometheus.version>
+      <prometheus.version>1.3.10</prometheus.version>
+      <jetty.version>9.4.57.v20241219</jetty.version>
   </properties>
   <dependencies>
     <dependency>
@@ -46,28 +47,56 @@
     </dependency>    
     <dependency>
       <groupId>io.prometheus</groupId>
-      <artifactId>simpleclient</artifactId>
+      <artifactId>prometheus-metrics-core</artifactId>
       <version>${prometheus.version}</version>
     </dependency>
     <dependency>
       <groupId>io.prometheus</groupId>
-      <artifactId>simpleclient_hotspot</artifactId>
+      <artifactId>prometheus-metrics-instrumentation-jvm</artifactId>
       <version>${prometheus.version}</version>
     </dependency>
     <dependency>
       <groupId>io.prometheus</groupId>
-      <artifactId>simpleclient_servlet</artifactId>
+      <artifactId>prometheus-metrics-exporter-servlet-javax</artifactId>
       <version>${prometheus.version}</version>
     </dependency>
     <dependency>
-      <groupId>org.eclipse.jetty</groupId>
-      <artifactId>jetty-server</artifactId>
-      <scope>provided</scope>
+      <groupId>io.prometheus</groupId>
+      <artifactId>prometheus-metrics-exporter-httpserver</artifactId>
+      <version>${prometheus.version}</version>
+    </dependency>
+    <dependency>
+        <groupId>io.prometheus</groupId>
+        <artifactId>prometheus-metrics-exposition-formats</artifactId>
+        <version>${prometheus.version}</version>
+    </dependency>
+    <dependency>
+      <groupId>io.prometheus</groupId>
+      <artifactId>prometheus-metrics-config</artifactId>
+      <version>${prometheus.version}</version>
+    </dependency>
+    <dependency>
+        <groupId>org.eclipse.jetty</groupId>
+        <artifactId>jetty-server</artifactId>
+        <version>${jetty.version}</version>
+    </dependency>
+    <dependency>
+        <groupId>org.eclipse.jetty</groupId>
+        <artifactId>jetty-servlet</artifactId>
+        <version>${jetty.version}</version>
+    </dependency>
+    <!-- You likely don't need this, but if you do, here's the correct syntax -->
+    <dependency>
+        <groupId>org.eclipse.jetty</groupId>
+        <artifactId>jetty-util</artifactId>
+        <version>${jetty.version}</version>
+        <!-- You could add a scope here if needed, e.g., <scope>provided</scope> -->
     </dependency>
     <dependency>
-      <groupId>org.eclipse.jetty</groupId>
-      <artifactId>jetty-servlet</artifactId>
-      <scope>provided</scope>
+        <groupId>javax.servlet</groupId>
+        <artifactId>javax.servlet-api</artifactId>
+        <version>3.1.0</version>
+        <scope>provided</scope>
     </dependency>
     <dependency>
       <groupId>org.mockito</groupId>