[FEATURE] Show why we cannot start detector

[kaituo]

Is your feature request related to a problem?
Currently, we don't show the reason why we cannot start a detector:

% curl -X POST localhost:9200/_opendistro/_anomaly_detection/detectors/5Ri6jYkBrL2utYVAN4Yf/_start
{"error":{"root_cause":[{"type":"status_exception","reason":"Fail to start detector"}],"type":"status_exception","reason":"Fail to start detector"},"status":500}%    

The actual error is the custom index is configured for ultrawarm storage, which leads to the write error we see

[2023-10-05T21:11:13,694][ERROR][o.o.a.i.AnomalyDetectionIndices] [8a530cead3e005b3d9b3067cb44688f6] Failed to write dummy AD result to result index opensearch-ad-plugin-result-foo
ClusterBlockException[index [opensearch-ad-plugin-result-foo] blocked by: [TOO_MANY_REQUESTS/12/disk usage exceeded flood-stage watermark, index has read-only-allow-delete block];]
	at org.opensearch.cluster.block.ClusterBlocks.indicesBlockedException([ClusterBlocks.java:244](http://clusterblocks.java:244/))
	at org.opensearch.cluster.block.ClusterBlocks.indexBlockedException([ClusterBlocks.java:222](http://clusterblocks.java:222/))
	at org.opensearch.action.support.replication.TransportReplicationAction.blockExceptions([TransportReplicationAction.java:356](http://transportreplicationaction.java:356/))
	at org.opensearch.action.support.replication.TransportReplicationAction$ReroutePhase.doRun([TransportReplicationAction.java:885](http://transportreplicationaction.java:885/))
	at [org.opensearch.common.util.concurrent.AbstractRunnable.run](http://org.opensearch.common.util.concurrent.abstractrunnable.run/)([AbstractRunnable.java:52](http://abstractrunnable.java:52/))
	at org.opensearch.action.support.replication.TransportReplicationAction.runReroutePhase([TransportReplicationAction.java:252](http://transportreplicationaction.java:252/))
	at org.opensearch.action.support.replication.TransportReplicationAction.doExecute([TransportReplicationAction.java:247](http://transportreplicationaction.java:247/))
	at org.opensearch.action.support.replication.TransportReplicationAction.doExecute([TransportReplicationAction.java:110](http://transportreplicationaction.java:110/))
	at org.opensearch.action.support.TransportAction$RequestFilterChain.proceed([TransportAction.java:219](http://transportaction.java:219/))
	at org.opensearch.indexmanagement.rollup.actionfilter.FieldCapsFilter.apply(FieldCapsFilter.kt:118)
	at org.opensearch.action.support.TransportAction$RequestFilterChain.proceed([TransportAction.java:217](http://transportaction.java:217/))
	at org.opensearch.performanceanalyzer.action.PerformanceAnalyzerActionFilter.apply([PerformanceAnalyzerActionFilter.java:78](http://performanceanalyzeractionfilter.java:78/))
	at org.opensearch.action.support.TransportAction$RequestFilterChain.proceed([TransportAction.java:217](http://transportaction.java:217/))
	at org.opensearch.security.filter.SecurityFilter.apply0([SecurityFilter.java:232](http://securityfilter.java:232/))
	at org.opensearch.security.filter.SecurityFilter.apply([SecurityFilter.java:149](http://securityfilter.java:149/))

What solution would you like?
We need to show the error and suggest in UX to change result index or migrate from warm to hot .