Specifying the unit in storage parameter

Hi,

We can specify the unit when setting autovacuum_vacuum_cost_delay
GUC as follows.

    ALTER SYSTEM SET autovacuum_vacuum_cost_delay TO '80ms';

OTOH we cannot specify the unit when setting autovacuum_vacuum_cost_delay
as storage parameter as follows.

    CREATE TABLE test (col1 int) WITH (autovacuum_vacuum_cost_delay = '80ms');
    ERROR:  invalid value for integer option
"autovacuum_vacuum_cost_delay": 80ms

This is not user-friendly. I'd like to propose the attached patch which
introduces the infrastructure which allows us to specify the unit when
setting INTEGER storage parameter like autovacuum_vacuum_cost_delay.
Comment? Review?

Regards,

--
Fujii Masao