[Enhancement Request] Enabling testing of non-cloud packages with the latest software version.

Many of the integration package system tests do not use the product's latest (defined in `variants.yml`) docker image for testing.

The integration packages must be tested against all the latest software versions to remain compatible.

To tackle this, the below mentioned approach is expected

- Developers, as part of the local system run (`elastic-package system test`) are intimated there exist a major version of the product available.
- Developers are expected to do one of the following approach
- Update `variants.yml` with the information of the latest (major version) of the software package. If the test is successful, create a PR to permanently include the major version of the software in the `variants.yml`
- Add entry in the `validations.yml` to suppress the notification.

**Current Environment.**

- Elastic-package is the most used tool by an integration developer as part of package development and testing.
- Elastic-package has capabilities to validate the quality of the integration package. If a specific package does not meet the required capabilities, exclusions can be added to validation.yml file of the specific package
- Elastic-package tool is aware of the folder structure of the integration package through package-spec

**Requirement**

- Include (non-cloud) software version check as part of the Integration system test

Sample
```
DOCKERFILE=Dockerfile
IMAGE_LINE=$(grep -E '^FROM' $DOCKERFILE)
IMAGE_NAME=$(echo $IMAGE_LINE | awk -F':' '{print $1}' | awk '{print $2}')
IMAGE_TAG=$(echo $IMAGE_LINE | awk -F':' '{print $2}')

echo "Image name: $IMAGE_NAME"
echo "Current version: $IMAGE_TAG"

LATEST_VERSION=$(curl -s "https://registry.hub.docker.com/v2/repositories/library/$IMAGE_NAME/tags?page_size=100" | jq -r '.results[].name' | grep -E '^[0-9]+\.[0-9]+\.[0-9]+$' | sort -V | tail -n1)

echo "Latest version: $LATEST_VERSION"

echo "::set-output name=image-name::$IMAGE_NAME"
echo "::set-output name=current-version::$IMAGE_TAG"
echo "::set-output name=latest-version::$LATEST_VERSION"

```

- Add a new validation, with a validation code such that - if the package is not using the latest version of the software, an error is reported. This error can be ignored by adding a validation exclusion in the validation.yml file
- Record the test outcome as an artifact file.

```
--report-format json --report-output file
--report-format xUnit --report-output file
```

**Note:**
The existing validation settings in elastic-package make use of elastic's package-spec. Since these settings are only related to test (system test) , making use of package-spec validation approach may not be needed i guess. However, making use of a common (`validations.yml`) file may be helpful