backup: run every 2 days; retain for 2 weeks

[jsnshrmn]

Description

Reduce backup frequency and retention

Rationale

Our backups use too much disk space:

• every other day still provides plenty of restore times within our one week of event stream data
• backups older than two weeks are of limited utility because of the amount of data loss due to the event data stream only going back ~7 days

Phabricator Ticket

https://phabricator.wikimedia.org/T350295

How Has This Been Tested?

I tested this locally, and it seems to work fine.

Screenshots of your changes (if appropriate):

Types of changes

What types of changes does your code introduce? Add an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

[suecarmol]

LGTM!