I got answer from the support that there is no 'SHOW PARTITIONS' in Unity Catalog as "UC doesn't manage the partitions for tables".
They suggested for work around `LIST` command, this is what I was able to came up with.
The problem I see here, is for the end users working with the External Tables. They will need to run the query I guess on the table:
select * from table where part_1 = 'something' limit 1;
to be able to discover partitions :).
is this Yet Another Limitation? Databricks seems to be more limitations now and you need to talk to support to find out how to work with it.