##### SUMMARY
docker_image module is missing etc_hosts parameter even if this is documented and accepted by docker.build() as  of https://docker-py.readthedocs.io/en/stable/images.html

The same argument is accepted by docker_run but the lack of support here prevents us from building images when extra_hosts is needed.

I mention that the only reason why I propose using `etc_hosts` is in order to keep it in sync with already existing implementation from `docker_container` module which accepts `etc_hosts` which is translated to `extra_hosts` on docker-python-api.

I would personally prefer to use the same names as docker-api but this would require changing docker_container too.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
docker_image

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible-devel
```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below

```

##### OS / ENVIRONMENT
<!--- Provide all relevant information below, e.g. target OS versions, network device firmware, etc. -->


##### STEPS TO REPRODUCE
<!--- Describe exactly how to reproduce the problem, using a minimal test-case -->

<!--- Paste example playbooks or commands between quotes below -->
```yaml

```

<!--- HINT: You can paste gist.github.com links for larger files -->

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->


##### ACTUAL RESULTS
<!--- Describe what actually happened. If possible run with extra verbosity (-vvvv) -->

<!--- Paste verbatim command output between quotes -->
```paste below

```

- "Use C(local) to make sure that the image is already available on the local
         docker daemon, i.e. do not try to build, pull or load the image."
      - "Before Ansible 2.12, the value of this option will be auto-detected
         to be backwards compatible, but a warning will be issued if it is not
         explicitly specified. From Ansible 2.12 on, auto-detection will be disabled
         and this option will be made mandatory."
    type: str
    choices:
    - build
    - load
    - pull
    - local
    version_added: "2.8"
  build:
    description:
      - "Specifies options used for building images."
    type: dict
    suboptions:
      cache_from:
        description:
          - List of image names to consider as cache source.
        type: list
      dockerfile:
        description:
          - Use with state C(present) and source C(build) to provide an alternate name for the Dockerfile to use when building an image.
          - This can also include a relative path (relative to I(path)).
        type: str
      http_timeout:
        description:
          - Timeout for HTTP requests during the image build operation. Provide a positive integer value for the number of