[tracking] legacy features we could start issuing deprecation warnings for

[graciegoheen]

• data_tests: was added as an alias for tests: when we expanded "tests" to include unit tests. we could deprecate existing tests: property
• --resource-type and --select resource_type: are redundant. (env vars are useful for excluding resource types in specific environments)
• defining snapshots in yml is preferred over legacy way of defining snapshots in jinja blocks in sql files https://docs.getdbt.com/reference/resource-configs/snapshots-jinja-legacy?version=1.12
• --selector and --select selector: are redundant