feat: add postgresql classifier (#1536)

* add postgresql classifier
Signed-off-by: witchcraze <witchcraze@gmail.com>

* revert package dedup test upgrade

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

---------

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>
Co-authored-by: Alex Goodman <alex.goodman@anchore.com>

syft/pkg/cataloger/binary/test-fixtures/classifiers/positive/postgresql-9.5alpha1/postgres

@@ -0,0 +1,5 @@
+byteaout
+byteain
+?PostgreSQL 9.5alpha1 on x86_64-unknown-linux-gnu, compiled by gcc (Debian 4.9.2-10) 4.9.2, 64-bit
+/tmp/buildd/postgresql-9.5-9.5~alpha1/build/../src/backend/utils/adt/windowfuncs.c
+argument of ntile must be greater than zero