Automatic merge from submit-queue (batch tested with PRs 42895, 45940)
[Federation] Automate configuring nameserver in cluster-dns for CoreDNS provider
Addresses issue #42894#42822
**Release note**:
```
[Federation] CoreDNS server will be automatically added to nameserver resolv.conf chain When using CoreDNS as dns provider for federation during federation join.
```
cc @madhusudancs @kubernetes/sig-federation-bugs
Added support for AAAA record for coredns and included unit test.
Fixed function names in comments for Google and AWS tests to match
actual test name in this area.
There can be multiple DNS resource records for a given name. They can
vary by type, ttl, rrdata and a number of various other parameters. It
is incorrect to return a single resource record for a given name.
This change updates the Get interface to return multiple records for a given
name and uses this list in the federated service controller to perform
DNS operations.
This will allow us to pass e.g. a ResourceRecordChangeset, rather than a
ResourceRecordChangeset, the parent ResourceRecordSets, and the
grandparent Zone.
Laying the groundwork for simplifying / optimizing the federation logic.
Although Google Cloud DNS requires strict add & remove calls, most
dnsproviders actually support upsert, and an add & remove is much more
expensive (primarily because of the need to fetch the pre-image).
Add support for 'upsert' operations, which don't require the pre-image,
and simply overwrite the existing record. This is much cheaper on
Amazon Route53, for example.
Automatic merge from submit-queue
dnsprovider: Add IsEmpty method
When batching changes, it is often handy to know whether a changeset
IsEmpty, and thus does not need to be Apply-ed.
```release-note
NONE
```
