Mark topology-based delivery services as available in Traffic Monitor

[zrhoffman]

What does this PR (Pull Request) do?

• This PR fixes Traffic Monitor marks topology-based delivery services as unavailable #4921 by adding topologies' cachegroups' servers to the delivery service servers map in todata.getDeliveryServiceServers().

Which Traffic Control components are affected by this PR?

• Documentation
• Traffic Monitor

What is the best way to verify this PR?

1. Make topology-based delivery service
2. Perform CDN snapshot
3. Look at Traffic Monitor logs. Lines to look for:

trafficmonitor_1            | 1595954995.290 host="demo1", type=Delivery Service, available=true, msg="available caches"
trafficmonitor_1            | 1595954995.290 host="demo1", type=DELIVERYSERVICE, available=true, msg="REPORTED - available"

If this is a bug fix, what versions of Traffic Control are affected?

• master (cc6f339)

The following criteria are ALL met by this PR

• This PR includes tests
• This PR includes documentation
• This PR includes an update to CHANGELOG.md
• This PR includes any and all required license headers
• This PR does not include a database migration
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

[shamrickus]

LGTM

• Docs build
• TM tests pass
• Topology based delivery services are correctly reported in TM