Support new queryable "_tier" metadata field (#5606) (#5608)

Co-authored-by: Steve Gordon <sgordon@hotmail.co.uk>

Author: github-actions[bot]

src/Nest/Search/FieldCapabilities/FieldCapabilitiesResponse.cs

@@ -65,6 +65,7 @@ public class FieldTypes : IsADictionaryBase<string, FieldCapabilities>
 		public FieldCapabilities Short => BackingDictionary.TryGetValue("short", out var f) ? f : null;
 		public FieldCapabilities Source => BackingDictionary.TryGetValue("_source", out var f) ? f : null;
 		public FieldCapabilities Text => BackingDictionary.TryGetValue("text", out var f) ? f : null;
+		public FieldCapabilities Tier => BackingDictionary.TryGetValue("_tier", out var f) ? f : null;
 		public FieldCapabilities TokenCount => BackingDictionary.TryGetValue("token_count", out var f) ? f : null;
 		public FieldCapabilities Type => BackingDictionary.TryGetValue("_type", out var f) ? f : null;
 		public FieldCapabilities Uid => BackingDictionary.TryGetValue("_uid", out var f) ? f : null;