Use pgstat_progress_update_multi_param instead of single param update

Hi,

While reviewing progress reporting for COPY command patches [1], a
point on using pgstat_progress_update_multi_param instead of
pgstat_progress_update_param wherever possible was suggested in [1].
We could do multiple param updates at once with a single API than
doing each param update separately. The advantages are - 1) reducing
few function calls making the code look cleaner 2) atomically updating
multiple parameters at once within a single backend write critical
section i.e. incrementing st_changecount at once in a critical
section instead of doing it for each param separately.

Attached is a patch that replaces some subsequent multiple
update_param calls with a single update_multi_param.

Thoughts?

[1] - https://www.postgresql.org/message-id/CALj2ACXQrFM%2BDSN9xr%3D%2ByRotBufnC_xgG-FQ6VXAUZRPihZAew%40mail.gmail.com

With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com