[improve][pip] PIP-301: Introduce LoadBalanceResources to unify the load-date CRUD

pip/pip-301.md

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+# Background knowledge
+
+The following z-nodes store the load and quota data about loadbalance. And the CRUD about them are handled by `localMetadataStore`, not `configurationMetadataStore`.
+* `/loadbalance/bundle-data`
+* `/loadbalance/broker-time-average`
+* `/loadbalance/resource-quota`
+
+Currently, the access about the above z-nodes are distributed everywhere. It's very easy to call the the wrong `configurationMetadataStore` to handle them, e.g.:
+* [[fix] [broker] remove bundle-data in local metadata store.](https://github.com/apache/pulsar/pull/21078)
+
+# Motivation
+
+Refactor the access code about balance/load data
+
+# Goals
+
+## In Scope
+
+Introduce `LoadBalanceResources` to unify the CRUD about balance/load data.
+
+## Out of Scope
+
+None
+
+# High Level Design
+
+Introduce `LoadBalanceResources` which has three inner class:
+* `BundleDataResources`
+* `BrokerTimeAverageResources`
+* `QuotaResources`
+
+# Detailed Design
+
+## Design & Implementation Details
+
+```java
+public class LoadBalanceResources {
+    public static final String BUNDLE_DATA_BASE_PATH = "/loadbalance/bundle-data";
+    public static final String BROKER_TIME_AVERAGE_BASE_PATH = "/loadbalance/broker-time-average";
+    public static final String RESOURCE_QUOTA_BASE_PATH = "/loadbalance/resource-quota";
+
+    private final BundleDataResources bundleDataResources;
+
+    public LoadBalanceResources(MetadataStore store, int operationTimeoutSec) {
+        bundleDataResources = new BundleDataResources(store, operationTimeoutSec);
+    }
+
+    public static class BundleDataResources extends BaseResources<BundleData> {
+        public BundleDataResources(MetadataStore store, int operationTimeoutSec) {
+            super(store, BundleData.class, operationTimeoutSec);
+        }
+        // ...
+    }
+
+    public static class BrokerTimeAverageResources extends BaseResources<TimeAverageBrokerData> {
+        public BrokerTimeAverageResources(MetadataStore store, int operationTimeoutSec) {
+            super(store, TimeAverageBrokerData.class, operationTimeoutSec);
+        }
+        // ...
+    }
+
+    public static class QuotaResources extends BaseResources<ResourceQuota> {
+        public QuotaResources(MetadataStore store, int operationTimeoutSec) {
+            super(store, ResourceQuota.class, operationTimeoutSec);
+        }
+        // ...
+    }
+}
+```
+
+## Public-facing Changes
+
+None
+
+### Public API
+
+None
+
+# Backward & Forward Compatibility
+
+None
+
+# Links
+
+* Mailing List discussion thread: https://lists.apache.org/thread/7ngw9dc62tj2c4c5484dgsnlwgtstpbj
+* Mailing List voting thread: https://lists.apache.org/thread/26dc8r6hnp7owdsq1hpzb48g8vlfrtxt