Change scorecard values for total item and properties from 50th percentile to Mean

[rosalieper]

Describe the changes

	1. On the Platform Summary dashboard in Google Cloud the scorecards total items and total properties
	are configured to 50th percentile instead of Mean and therefore show incorrect numbers not matching the charts ?
	2. I made the change on the google cloud dashboard and downloaded the json with
	which I then updated these files?

This is what I need help with

Please confirm this has no bomb in it and can be deployed to production.

Link to Phabricator

https://phabricator.wikimedia.org/T369347

[AndrewKostka]

It might be easier if we only replace REDUCE_PERCENTILE_50 with REDUCE_MEAN in the JSON for the two relevant scorecards. I've noticed issues with subsequent Terraform runs always trying to re-apply any default values.