Add installation creation date to Service Ping

What does this MR do and why?

Both the Customer Success and Product Data Insights teams have expressed interest in installation creation dates, which are currently not recorded.

This MR adds a metric called installation_creation_date that will get the created_at timestamp from the root user of the installation. Based on this Customer Success and Product Data Insights can calculate the timespans that they are missing.

How to set up and validate locally

1. Run bin/rake gitlab:usage_data:dump_sql_in_json
2. Verify that the installation_creation_date is present and has a value.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #379410 (closed)