No Nest support for DynamicTemplate.MatchPattern (match_pattern property)

[jacob-123]

NEST/Elasticsearch.Net version:
5.6.2 (Not present @5.6.3 as well
Elasticsearch version:
5.6.4
Description of the problem including expected versus actual behavior:
JSON:
"my_dynamic_mapping_string": {
"match_pattern": "regex",
"path_match": "foo[0-9]",
"match_mapping_type": "string",
"fielddata": true,
"copy_to": "bar"
Expected Nest:
.DynamicTemplate("my_dynamic_mapping_string", dm => dm
.MatchMappingType("string")
.PathMatch("foo[0-9]")
.MatchPattern("regex")
.Mapping(m => ...)
);
Actual Nest gets an error :
Error 18 'Nest.DynamicTemplateDescriptor' does not contain a definition for 'MatchPattern' and no extension method 'MatchPattern' accepting a first argument of type 'Nest.DynamicTemplateDescriptor' could be found (are you missing a using directive or an assembly reference?)

Steps to reproduce:

1. Use Nest 5.6.x
2. Create a dynamic Mapping using the above Dynamic Template :
   client.Map(x => x.Index(indexName).Type(typeName)
   .DynamicTemplates(dt =>
   dt.DynamicTemplate("my_dynamic_mapping_string", dm =>
   dm.MatchMappingType("string")
   .PathMatch("foo[0-9]")
   .MatchPattern("regex")
   .Mapping(m => ...))

Provide ConnectionSettings (if relevant):
Not Relevant
Provide DebugInformation (if relevant):
Not Relevant

[russcam]

Thanks @jacob-123, I've opened #3374 to address