Add filter dict_kv (#1264)

- Add filter `dict_kv` which returns a single key-value pair dictionary created from two arguments

Example 1

```
- hosts: localhost
  gather_facts: false
  vars:
    myvar: myvalue
  tasks:
  - debug:
      msg: "{{ myvar | dict_kv('thatsmyvar') }}"

OUTPUT:
ok: [localhost] => {
    "msg": {
        "thatsmyvar": "myvalue"
    }
}
```

Example 2

```
- hosts: localhost
  gather_facts: false
  vars:
    common_config:
      type: host
      database: all
    myservers:
    - server1
    - server2
  tasks:
  - debug:
      msg: "{{ myservers | map('dict_kv', 'server') | map('combine', common_config) }}"

OUTPUT:
ok: [localhost] => {
    "msg": [
        {
            "database": "all",
            "server": "server1",
            "type": "host"
        },
        {
            "database": "all",
            "server": "server2",
            "type": "host"
        }
    ]
}
```

tests/integration/targets/filter_dict_kv/aliases

@@ -0,0 +1,2 @@
+shippable/posix/group2
+skip/python2.6  # filters are controller only, and we no longer support Python 2.6 on the controller

tests/integration/targets/filter_dict_kv/tasks/main.yml

@@ -0,0 +1,10 @@
+---
+####################################################################
+# WARNING: These are designed specifically for Ansible tests       #
+# and should not be used as examples of how to write Ansible roles #
+####################################################################
+
+- name: test dict_kv filter
+  assert:
+    that:
+      - "('value' | community.general.dict_kv('key')) == {'key': 'value'}"