Add frontend and backend dependabot duty to on-call roster

[snesm]

Problem statement

Today the on-call roster reports:

GitHub Actions [9:35 AM] CDCgov/prime-reportstream PagerDuty On-Call PRIME ReportStream :exclamation:Now: Jeremy P*** ReportStream Dependabot :exclamation:Now: Arnej D**** ReportStream Deployment :exclamation:Now: Brick G**** ReportStream Front End Checks :exclamation:Now: Etan B******

Arnej is not responsible for dependabot frontend PR's.

It would be desirable to have an on-call roster of both frontend and backend engineers listed for contact.

What you need to know

[Links to documents, workflows, or list of key people and contact info]

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Acceptance criteria

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To do

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