Create customer facing templates for RDS upgrades

[cweibel]

In order to notify our customers that they have retiring instance types and database engine versions, we need to identify the databases impacted and provide upgrade guidance

• Customer dbs on t2 and m4 we need to move for reserved instance costs, being retired by April by AWS
• Customer dbs on postgres 11.x will cost us starting april 1 (https://docs.aws.amazon.com/AmazonRDS/latest/PostgreSQLReleaseNotes/postgresql-release-calendar.html)
• Customers dbs on mysql 5.7.x will cost us starting april 1 (https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/MySQL.Concepts.VersionMgmt.html)

Tasks

• [x] Create email template for engine version upgrades
• [x] Create email template for instance type upgrades
• [x] Get language approved by the Business team
• [x] Create script to identify customers/platform impacted rds instances
• [x] Review with the Success team

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Security considerations

There should be no changes to security boundaries, practices, documentation, risk that arise directly from this story

Implementation sketch

Pseudo code:

    if (family = t2,m4) and (pg 11.19 or mysql 5.7.32)
        customer needs to upgrade instance type and perform engine upgrade
    elseif  !(family = t2,m4) and (pg 11.19 or mysql 5.7.32)
        customer needs to upgrade engine
    elseif  (family = t2,m4) and !(pg 11.19 or mysql 5.7.32)
        customer needs to upgrade instance type
    else
        db is fine, leave alone
    end if