Fix: Increase Cohere integration test timeout to 120s (#4767)

Cohere integration tests are failing in CI with "Read timed out" errors.
The Cohere connector was using default timeout (30s) which is insufficient
for CI environment where API calls can take 60-90+ seconds.

Changes:
- Add client_config to Cohere connector with 120s connection_timeout and read_timeout
- Add service reachability check for api.cohere.ai to gracefully skip tests when service is unavailable

Fixes flaky test failures in:
- testBM25WithCohere
- testBM25WithCohereUsingLlmResponseField

Signed-off-by: rithin-pullela-aws <rithinp@amazon.com>

Author: rithinpullela

plugin/src/test/java/org/opensearch/ml/rest/RestMLRAGSearchProcessorIT.java

@@ -255,6 +255,11 @@ public class RestMLRAGSearchProcessorIT extends MLCommonsRestTestCase {
         + "    \"description\": \"The connector to Cohere's public chat API\",\n"
         + "    \"version\": \"1\",\n"
         + "    \"protocol\": \"http\",\n"
+        + "    \"client_config\": {\n"
+        + "        \"max_connection\": 30,\n"
+        + "        \"connection_timeout\": 120,\n"
+        + "        \"read_timeout\": 120\n"
+        + "    },\n"
         + "    \"credential\": {\n"
         + "        \"cohere_key\": \""
         + COHERE_KEY
@@ -1079,8 +1084,8 @@ public void testBM25WithBedrockWithConversation() throws Exception {
     }
 
     public void testBM25WithCohere() throws Exception {
-        // Skip test if key is null
-        if (COHERE_KEY == null) {
+        // Skip test if key is null or service is unreachable
+        if (COHERE_KEY == null || !isServiceReachable("api.cohere.ai")) {
             return;
         }
         Response response = createConnector(COHERE_CONNECTOR_BLUEPRINT);
@@ -1131,8 +1136,8 @@ public void testBM25WithCohere() throws Exception {
     }
 
     public void testBM25WithCohereUsingLlmResponseField() throws Exception {
-        // Skip test if key is null
-        if (COHERE_KEY == null) {
+        // Skip test if key is null or service is unreachable
+        if (COHERE_KEY == null || !isServiceReachable("api.cohere.ai")) {
             return;
         }
         Response response = createConnector(COHERE_CONNECTOR_BLUEPRINT);