Monitor PostgreSQL flavor in usage ping

What does this MR do and why?

This MR adds PostgreSQL flavor to usage data metrics.

Flavor can be one of :

• "Amazon Aurora PostgreSQL"
• "PostgreSQL on Amazon RDS"
• "Cloud SQL for PostgreSQL"
• "Azure Database for PostgreSQL - Flexible Server"
• "Azure Database for PostgreSQL - Single Server"
• "null" (if we can't detect what flavor is used)

https://gitlab.com/gitlab-services/version-gitlab-com/-/merge_requests/637 will add new database column to VersionApp where we'll store this new data.

Related to https://gitlab.com/gitlab-org/database-team/team-tasks/-/issues/218.

How to set up and validate locally

1. In rails console execute the following

   > usage_data = ServicePing::BuildPayloadService.new.execute
   > usage_data[:database]

2. For standard PostgreSQL you should see

   > {:adapter=>"postgresql", :version=>"12.9", :pg_system_id=>6976470454675971923, :flavor=>nil}

3. To simulate Aurora first create the following function in your database

   > CREATE OR REPLACE FUNCTION AURORA_VERSION() RETURNS TEXT
   LANGUAGE plpgsql
   AS $$
   BEGIN
    RETURN '1.2.3';
   END;
   $$;

   This will result in

   > {:adapter=>"postgresql", :version=>"12.9", :pg_system_id=>6976470454675971923, :flavor=>"Amazon Aurora PostgreSQL"}

4. To simulate Azure Database for PostgreSQL - Single Server create the following database

   > CREATE DATABASE azure_maintenance;

   This will result in

   > {:adapter=>"postgresql", :version=>"12.9", :pg_system_id=>6976470454675971923, :flavor=>"Azure Database for PostgreSQL - Single Server"}

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.