Add support to filter test configurations depending on the subscription level of the running stack

[mrodm]

The elastic-package has been updated to allow users to start the Elastic stack with different subscription levels (e.g. basic) since the pull request #2501. By default, the subscription used in the Elastic stacks managed by elastic-package is trial.

After adding new builds to test packages with the basic subscription in the integrations repository, there is a package failure due to a processor not available with that subscription level (more info at elastic/integrations#13503)

To address this, we propose adding a new setting in the test configuration files to specify the required subscription level. This setting could be added as follows:

@@ -1,3 +1,4 @@
+subscription: platinum
 multiline:
   first_line_pattern: "^\\d{4}\\/\\d{2}\\/\\d{2} "
 fields:
   "@timestamp": "2020-04-28T11:07:58.223Z"
 dynamic_fields:
   "event.ingested": ".*"

Scenarios in test configuration:

• No subscription key: All test configurations without subscription setting are tested.
• subscription: basic: Test configurations with this subscription level will always be tested.
• subscription: platinum|enterprise: Test configurations with this subscription levels will only be tested if the stack subscription is trial.

This new setting in test configuration should be available for both pipeline and system tests.