Add validation to control script usage on connector (pre / post process function)

[brianf-aws]

Problem

There is no current way to make sure a user is not allowed to use a scriptService when using a connector. If I happen to have a user use my custom version of OpenSearch they would be able to create connectors without any guardrails to stop them from using a script.

Proposed solution

Use a cluster setting opensearch.plugins.ml.script.allowed_types : None | Painless to control how a user can create connectors.

we can add a check in the connectorAction to get a cluster setting while the connectorAction is getting initialized when the TransportCreateConnectorAction.doExecute action

[brianf-aws]

This should help alleviate pain point where user creates connector with painless script and if user attempts to perform prediction and then user runs into errors this is because of the compile step

https://github.com/opensearch-project/OpenSearch/blob/cd9d1382a9520600ac93e02d307ce63fb063ed6d/server/src/main/java/org/opensearch/script/ScriptService.java#L465-L467

Which only gets run After the ML Model returns a result and post processing occurs

ml-commons/common/src/main/java/org/opensearch/ml/common/connector/functions/preprocess/ConnectorPreProcessFunction.java

Lines 88 to 92 in 684627a

	protected String executeScript(ScriptService scriptService, String painlessScript, Map<String, Object> params) {
	Script script = new Script(ScriptType.INLINE, "painless", addDefaultMethod(painlessScript), Collections.emptyMap());
	TemplateScript templateScript = scriptService.compile(script, TemplateScript.CONTEXT).newInstance(params);
	return templateScript.execute();
	}

[brianf-aws]

Seems we can reuse the Same method to view if the scriptService is enabled

    public boolean isTypeEnabled(ScriptType scriptType) {
        return typesAllowed == null || typesAllowed.contains(scriptType.getName());
    }

Check from the Script Service to check just before the connector creation so it fails fast

https://github.com/opensearch-project/OpenSearch/blob/cd9d1382a9520600ac93e02d307ce63fb063ed6d/server/src/main/java/org/opensearch/script/ScriptService.java#L506-L508