change float4 to floating point about type of autovacuum_vacuum_insert_scale_factor

Hi

As shown below, the argument types of autovacuum_vacuum_insert_scale_factor and
toast.autovacuum_vacuum_insert_scale_factorare different from the others. 
---
autovacuum_vacuum_scale_factor, toast.autovacuum_vacuum_scale_factor (floating point)
autovacuum_vacuum_insert_scale_factor, toast.autovacuum_vacuum_insert_scale_factor (float4)
autovacuum_analyze_scale_factor (floating point)
autovacuum_vacuum_cost_delay, toast.autovacuum_vacuum_cost_delay (floating point)
https://www.postgresql.org/docs/devel/sql-createtable.html
---

In addition, there is this statement.
---
autovacuum_vacuum_insert_scale_factor (floating point)
https://www.postgresql.org/docs/devel/runtime-config-autovacuum.html#GUC-AUTOVACUUM-VACUUM-INSERT-SCALE-FACTOR
---

So, I thought it was better to be consistent with "floating point", and I created the patch.

A similar argument can be found here.
https://www.postgresql.org/message-id/CACZ0uYFf_p9BpbjLccx3CA=eM1Hk2Te=ULY4iptGLUhL-JxCPA@mail.gmail.com

Best Regards,
Shinya Kato