Change default value replace_fields to false in add_host_metadata processor

[kaiyan-sheng]

We added this new config parameter replace_fields into add_host_metadata processor in #20490 to make sure we have the ability to overwrite host.* fields or not. Right now, the default for replace_fields is true, which means add_host_metadata will overwrite host fields.

With recently added new fields for host inventory schema work and once these fields start getting used by UI, we need to make the breaking change to switch the default replace_fields value to false. This way, the new added host.* fields will not be overwritten.

[elasticmachine]

Pinging @elastic/integrations-platforms (Team:Platforms)

[botelastic]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.