Add alnum (text pattern) multi field to host.name and observer.name

The background is to make parts of the FQDN or hostname searchable.
Example:

```
POST _analyze
{
  "analyzer": "pattern",
  "text": "host55-bmc.example.net"
}
```

Output:

```json
{
  "tokens" : [
    {
      "token" : "host55",
      "start_offset" : 0,
      "end_offset" : 6,
      "type" : "word",
      "position" : 0
    },
    {
      "token" : "bmc",
      "start_offset" : 7,
      "end_offset" : 10,
      "type" : "word",
      "position" : 1
    },
    {
      "token" : "example",
      "start_offset" : 11,
      "end_offset" : 18,
      "type" : "word",
      "position" : 2
    },
    {
      "token" : "net",
      "start_offset" : 19,
      "end_offset" : 22,
      "type" : "word",
      "position" : 3
    }
  ]
}
```

schemas/host.yml

@@ -25,6 +25,10 @@
       level: core
       type: keyword
       short: Name of the host.
+      multi_fields:
+        - type: text
+          name: alnum
+          analyzer: pattern
       description: >
         Name of the host.
 

schemas/observer.yml

@@ -50,6 +50,10 @@
       level: extended
       type: keyword
       short: Custom name of the observer.
+      multi_fields:
+        - type: text
+          name: alnum
+          analyzer: pattern
       description: >
         Custom name of the observer.
 

scripts/generators/es_template.py

@@ -175,7 +175,7 @@ def entry_for(field):
                 if mf_type == 'keyword':
                     ecs_helpers.dict_copy_existing_keys(mf, mf_entry, ['normalizer', 'ignore_above'])
                 elif mf_type == 'text':
-                    ecs_helpers.dict_copy_existing_keys(mf, mf_entry, ['norms'])
+                    ecs_helpers.dict_copy_existing_keys(mf, mf_entry, ['norms', 'analyzer'])
                 field_entry['fields'][mf['name']] = mf_entry
 
     except KeyError as ex: