Update SAMPLE_FORMAT.md (#4585)
Update SAMPLE_FORMAT.md (#4585)

* Require IT as prefix or suffix for most tests
* Add **Preferred Dependencies** section

- [x] Please **merge** this PR for me once it is approved.

GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples