[terraform] Add DNS records for load balancers

Summary:
Address ENG-8430.

Added:

• Data source for Hosted Zone (sth like domain for which we add DNS records)
• DNS records for each service load balancer. Configured the same way as in AWS Console (A record; alias)

Docs:

• aws_route53_record
• aws_route53_zone

Test Plan:
Added import { ... } blocks:

import {
  to = aws_route53_record.service_load_balancer["Blob"]
  id = "Z************_blob.staging.comm********gies.org_A"
}
# ... the same for each service, similiarly for prod

Terraform plan for both staging and prod shown that resources are going to be imported, without diff.

Reviewers: will, kamil

Reviewed By: will

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12460