added GetSuggestion action classes

Signed-off-by: Dennis Toepker <toepkerd@amazon.com>

alerting/src/main/kotlin/org/opensearch/alerting/action/GetSuggestionsAction.kt

@@ -0,0 +1,15 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.alerting.action
+
+import org.opensearch.action.ActionType
+
+class GetSuggestionsAction private constructor() : ActionType<GetSuggestionsResponse>(NAME, ::GetSuggestionsResponse) {
+    companion object {
+        val INSTANCE = GetSuggestionsAction()
+        const val NAME = "cluster:admin/opensearch/alerting/suggestions/get" // TODO: is this an ok name to use?
+    }
+}

alerting/src/main/kotlin/org/opensearch/alerting/action/GetSuggestionsRequest.kt

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+package org.opensearch.alerting.action
+
+import org.opensearch.action.ActionRequest
+import org.opensearch.action.ActionRequestValidationException
+import org.opensearch.alerting.model.Monitor
+import org.opensearch.common.io.stream.StreamInput
+import org.opensearch.common.io.stream.StreamOutput
+import java.io.IOException
+
+class GetSuggestionsRequest : ActionRequest {
+    val monitorId: String?
+    val monitor: Monitor?
+
+    constructor(
+        monitorId: String?,
+        monitor: Monitor?
+    ) : super() {
+        this.monitorId = monitorId
+        this.monitor = monitor
+    }
+
+    @Throws(IOException::class)
+    constructor(sin: StreamInput) : this(
+        sin.readOptionalString(), // monitorId
+        if (sin.readBoolean()) {
+            Monitor.readFrom(sin) // monitor
+        } else null
+    )
+
+    override fun validate(): ActionRequestValidationException? {
+        return null
+    }
+
+    @Throws(IOException::class)
+    override fun writeTo(out: StreamOutput) {
+        out.writeOptionalString(monitorId)
+        if (monitor != null) {
+            out.writeBoolean(true)
+            monitor.writeTo(out)
+        } else {
+            out.writeBoolean(false)
+        }
+    }
+}

alerting/src/main/kotlin/org/opensearch/alerting/action/GetSuggestionsResponse.kt

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+package org.opensearch.alerting.action
+
+import org.opensearch.action.ActionResponse
+import org.opensearch.common.io.stream.StreamInput
+import org.opensearch.common.io.stream.StreamOutput
+import org.opensearch.common.xcontent.ToXContent
+import org.opensearch.common.xcontent.ToXContentObject
+import org.opensearch.common.xcontent.XContentBuilder
+import org.opensearch.rest.RestStatus
+import java.io.IOException
+
+class GetSuggestionsResponse : ActionResponse, ToXContentObject {
+    var suggestions: List<String>
+    var status: RestStatus
+    // TODO: do we need id, primaryTerm, seqNo, etc, what are they used for?
+
+    constructor(
+        suggestions: List<String>,
+        status: RestStatus,
+    ) : super() {
+        this.suggestions = suggestions
+        this.status = status
+    }
+
+    @Throws(IOException::class)
+    constructor(sin: StreamInput) : this(
+        sin.readStringList(), // suggestions
+        sin.readEnum(RestStatus::class.java), // RestStatus
+    )
+
+    @Throws(IOException::class)
+    override fun writeTo(out: StreamOutput) {
+        out.writeStringCollection(this.suggestions)
+        out.writeEnum(this.status)
+    }
+
+    @Throws(IOException::class)
+    override fun toXContent(builder: XContentBuilder, params: ToXContent.Params): XContentBuilder {
+        builder.startObject()
+            .field("suggestions", this.suggestions)
+
+        return builder.endObject()
+    }
+}