[Feature Request] Include TSDB related tests as part of the test

Adding two suggestions in the context of TSDB

- [TSDB Test Toolkit](https://github.com/elastic/TSDB-migration-test-kit) is a very important toolset to validate the possibility of data drop when datasets are TSDB enabled. Can we perform TSDB test toolkit run as part of the system test for datasets with `index_mode: "time_series"` ?
- Include an additional check (`elastic-package check`)to validate If there exists `type: metrics` in `manifest.yml`, there is also `index_mode: "time_series"` . This can be overridden by a flag --no-tsdb. This ensures that all future contributions are having `index_mode: time_series`

Start with the existing system-test entry points and the `elastic-package check` command. Review the TSDB Test Toolkit and the `manifest.yml` fields described in the issue, then determine how `index_mode: "time_series"` and the `--no-tsdb` override should be validated. Done means TSDB datasets run the toolkit and metrics manifests receive the additional check.

Written by the indexing model from the issue text.