When create template v2. mappings will add _doc. This will cause the created template to be inconsistent with the queried template.

In template class, add mappingsEquals method, to deal with this case.

reproduced:
MetadataIndexTemplateServiceTests.testAddComponentTemplate
when mappings are not null, the case will failed.

```
        Template template = new Template(
            Settings.builder().build(),
            new CompressedXContent("{\"properties\":{\"@timestamp\":{\"type\":\"date\"}}}"),
            ComponentTemplateTests.randomAliases()
        );
        ComponentTemplate componentTemplate = new ComponentTemplate(template, 1L, new HashMap<>());
```

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>
# Conflicts:
#	server/src/test/java/org/elasticsearch/cluster/metadata/MetadataIndexTemplateServiceTests.java