feat(libs/emails): Add retry with backoff for email-sender

Because:
 - We want to enable retrying an email send if the send fails

This Commit:
 - Adds a new retryWithBackoff for accounts-email-sender
 - Adds configuration to change maxRetries, backoffMs, and
   ignoreTempaltes
 - Adds tests for new functionality

Closes: FXA-12591

Author: nshirley