fix(core): Resolve TypeScript strict mode and ES client API compatibility issues for v3.0.0

- Fix ES client v8+ API: use document/doc instead of body for index/update operations
- Add type assertions (as any) for ES client ILM, template, and search APIs
- Fix strict null checks with proper undefined handling (nullish coalescing)
- Fix MetricsCollector interface to match required method signatures
- Fix Logger.error signature compatibility in plugins
- Resolve TermsQuery type index signature conflict
- Remove sourceMap from tsconfig (handled by tsbuild with inlineSourceMap)

ts/core/observability/metrics.ts

@@ -529,6 +529,42 @@ export class MetricsCollector {
     return histogram;
   }
 
+  /**
+   * Record a counter increment (convenience method for plugins)
+   */
+  recordCounter(name: string, value: number = 1, labels: Labels = {}): void {
+    let counter = this.registry.get(name) as Counter | undefined;
+    if (!counter) {
+      counter = new Counter(name, `Counter: ${name}`, Object.keys(labels));
+      this.registry.register(counter);
+    }
+    counter.inc(labels, value);
+  }
+
+  /**
+   * Record a histogram observation (convenience method for plugins)
+   */
+  recordHistogram(name: string, value: number, labels: Labels = {}): void {
+    let histogram = this.registry.get(name) as Histogram | undefined;
+    if (!histogram) {
+      histogram = new Histogram(name, `Histogram: ${name}`, Object.keys(labels));
+      this.registry.register(histogram);
+    }
+    histogram.observe(value, labels);
+  }
+
+  /**
+   * Record a gauge value (convenience method for plugins)
+   */
+  recordGauge(name: string, value: number, labels: Labels = {}): void {
+    let gauge = this.registry.get(name) as Gauge | undefined;
+    if (!gauge) {
+      gauge = new Gauge(name, `Gauge: ${name}`, Object.keys(labels));
+      this.registry.register(gauge);
+    }
+    gauge.set(value, labels);
+  }
+
   /**
    * Export all metrics in Prometheus format
    */