fix: Rename gauge to db.pool.connections to avoid Prometheus _total suffix

The new Prometheus Java client (used by PrometheusMeterRegistry in
micrometer 1.14.5) strips the _total suffix from metric names because
it is reserved for counters. The gauge db.connections.total was being
sanitized to db_connections, causing the test to fail when looking for
db_connections_total in the scrape output.

Renamed to db.pool.connections which exports as db_pool_connections
in Prometheus format, avoiding suffix conflicts.

Author: RajdeepKushwaha5

openmetadata-service/src/main/java/org/openmetadata/service/monitoring/OpenMetadataMetrics.java

@@ -50,7 +50,7 @@ public OpenMetadataMetrics(MeterRegistry meterRegistry) {
             .sla(LATENCY_SLA_BUCKETS)
             .register(meterRegistry);
 
-    Gauge.builder("db.connections.total", () -> poolTotalConnections())
+    Gauge.builder("db.pool.connections", () -> poolTotalConnections())
         .description("Total connections in the database connection pool")
         .register(meterRegistry);
 

openmetadata-service/src/test/java/org/openmetadata/service/monitoring/OpenMetadataMetricsTest.java

@@ -33,8 +33,8 @@ void dbConnectionsTotalReflectsHikariCPPoolSize() {
 
     new OpenMetadataMetrics(registry);
 
-    Gauge total = registry.find("db.connections.total").gauge();
-    assertNotNull(total, "db.connections.total gauge should be registered");
+    Gauge total = registry.find("db.pool.connections").gauge();
+    assertNotNull(total, "db.pool.connections gauge should be registered");
     assertEquals(20.0, total.value(), 0.01, "Should equal active + idle");
 
     activeConnections.set(10);
@@ -50,8 +50,8 @@ void dbConnectionsTotalReflectsHikariCPPoolSize() {
   void dbConnectionsTotalReturnsZeroWithoutHikariCP() {
     new OpenMetadataMetrics(registry);
 
-    Gauge total = registry.find("db.connections.total").gauge();
-    assertNotNull(total, "db.connections.total gauge should be registered");
+    Gauge total = registry.find("db.pool.connections").gauge();
+    assertNotNull(total, "db.pool.connections gauge should be registered");
     assertEquals(0.0, total.value(), 0.01, "Should be zero when HikariCP metrics are absent");
   }
 
@@ -71,10 +71,10 @@ void prometheusScrapeExposesDbConnectionsTotal() {
 
     String scrape = promRegistry.scrape();
     assertTrue(
-        scrape.contains("db_connections_total"),
-        "Prometheus scrape should contain db_connections_total metric");
+        scrape.contains("db_pool_connections"),
+        "Prometheus scrape should contain db_pool_connections metric");
     assertTrue(
-        scrape.contains("# TYPE db_connections_total gauge"),
-        "db_connections_total should be exposed as a gauge type");
+        scrape.contains("# TYPE db_pool_connections gauge"),
+        "db_pool_connections should be exposed as a gauge type");
   }
 }