[CI][upgrade tests] Add support to run upgrade tests (policy and system tests).

Part of https://github.com/elastic/elastic-package/issues/1831

Add support to run upgrade tests as described in https://github.com/elastic/elastic-package/issues/1831 for policy and system tests.

The process could vary depend on how long it takes to run all these upgrade tests along with the current policy and system tests.

In the following issues it is detailed how these upgrade tests are defined and enabled (by default they are disabled):
- https://github.com/elastic/elastic-package/issues/3150
- https://github.com/elastic/elastic-package/issues/3151

Options to assess for this issue:
- Run upgrade tests in Pull Requests if a new comment is posted in the Pull Request.
- Similar to the current process to test with another Elastic stack version `/test stack `: https://github.com/elastic/integrations/blob/main/docs/ci_pipelines.md#pull-requests-and-pushes-to-specific-branches
- Run these upgrade tests just once in daily or weekly builds.
- Add support to select which tests need to be tested
- This will be interesting for packages like `network_traffic`, `zeek`, `aws` among others that define a large number of tests.