gcp: refactor disk iops and throughput

[afumagalli98]

check disk recommendation and use the following logic:

• iops r/w must be limit for zonal Persistent Disk and multiply for the disk size (GB)

• if the result of size and limit is greater than this use the table values as max

• the throughput is referenced to this table

[afumagalli98]

Update: use only the table of max limits to create disk recommendations ( 2th point )