Adds job to mute promotions via CSV

What's this PR do?

This pull request adds a new file import type, mute-promotions, that sets the promotions_muted_at field for the users in a given CSV, deleting their Customer.io profile.

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Relevant tickets

References Pivotal #176771195.

Checklist

[x] This PR has been added to the relevant Pivotal card.
[ ] Documentation added for new features/changed endpoints.
[ ] Added appropriate feature/unit tests.

DoSomething / chompy

Adds job to mute promotions via CSV #200

What's this PR do?

How should this be reviewed?

Any background context you want to provide?

Relevant tickets

Checklist