When a shard becomes search active then trigger a refresh instead of waiting for the next scheduled refresh.
The `IndexShard#awaitShardSearchActive(...)` method registers a refresh listener and then often waits for the refresh scheduler to trigger a refresh. By default this is one second. In order to avoid increasing the query time of the Search API, the mentioned method should trigger a refresh instead for waiting it to happen.

As part of this change we also need to disable the refresh scheduler completely. Otherwise we run at risk of running two refreshes next after each other. One triggered from making shard search active and one from the refresh scheduler.  



server/src/test/java/org/elasticsearch/index/shard/IndexShardTests.java
new MockLogAppender.SeenEventExpectation(
                    "should see second flush returning since it will not wait for the ongoing flush",
                    Engine.class.getCanonicalName(),
                    Level.TRACE,
                    "detected an in-flight flush, not blocking to wait for it's completion"
                )
            );
            shard.flushOnIdle(0);
            assertBusy(mockLogAppender::assertAllExpectationsMatched);
            
            assertFalse(shard.flush(new FlushRequest().waitIfOngoing(false).force(false)));
            
            readyToCompleteFlushLatch.countDown();
            
            mockLogAppender.addExpectation(
                new MockLogAppender.SeenEventExpectation(
                    "should see first flush releasing lock",
                    Engine.class.getCanonicalName(),
                    Level.TRACE,
                    "released flush lock"
                )
            );
            assertBusy(mockLogAppender::assertAllExpectationsMatched);
            
            assertTrue(shard.isActive());
            
            assertTrue(shard.flush(new FlushRequest()));
            closeShards(shard);
        } finally {
            Loggers.removeAppender(LogManager.getLogger(Engine.class), mockLogAppender);