Sync only exposures is not working properly

[Vitor-Avila]

After the implementation of #130, users should be able to trigger a sync only for exposures, by using the --select parameter and filtering for a tag that isn't used on dbt.

However, this approach is not working properly - after running below command, no changes are applied to the exposures.yml file:

preset-cli --workspaces=$PRESET_WORKSPACE \
superset sync dbt-core $MANIFEST_PATH \
--project=$PROJECT_NAME --target=$TARGET_NAME --profiles=$PROFILES_PATH \
--exposures=$EXPOSURES_PATH \
--import-db \
--select tag:not-existent

Also, it would be beneficial to implement a particular command to allow this approach (something like --exposures-only) rather than having to use the --select filter and excluding everything.