Postgres Upsert command does not support specifying index predicate for partial unique indices

[smaximov]

Currently there's no way to generate the following "upsert" query (which uses partial unique index) using the Upsert command:

# Assuming this unique partial index exists:
# CREATE UNIQUE INDEX idx ON my_table (some_column) WHERE another_column = 'foo'

INSERT INTO my_table(...) VALUES(...)
ON CONFLICT (some_column) WHERE another_column = 'foo'
DO ...

Although we can set "some_column" as conflict_target, it won't work because the user can't specify the partial index predicate (which is necessary to infer the partial index).