Apply data-checksum worker throttling parameters

Apply data-checksum worker throttling parameters

The DataChecksumsWorker accepts cost_delay and cost_limit parameters
from pg_enable_data_checksums() so users can throttle the I/O caused
by enabling checksums.  Due to the API for setting the cost parameters
changing between when the code was written, and when it was committed
the new cost update function call was omitted and thus the parameters
were silently ignored.

Fix by calling VacuumUpdateCosts() after assigning the parameters
(both during worker startup and on the runtime cost-update path), and
by leaving the page-cost weights at their GUC-controlled defaults.

Author: Satyanarayana Narlapuram <satyanarlapuram@gmail.com>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Discussion: https://postgr.es/m/CAHg+QDeevH6aTyWdXYBJW0wOmfoZy66gDi5TfinK_dXeCrHQLg@mail.gmail.com