Batch DNS refresh requests on host renames

[gbrodman]

Some hosts can have more than 100k domains linked to them so we probably don't want to insert all those entries at once.

As far as I'm aware this hasn't been an issue in practice, but we should still do it just in case.

Self assessment D.5 number 16

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This change is 

[CydeWeys]

@CydeWeys made 1 comment.
Reviewable status: 0 of 3 files reviewed, 1 unresolved discussion (waiting on gbrodman).

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core/src/main/java/google/registry/dns/RefreshDnsOnHostRenameAction.java line 77 at r1 (raw file):

  private void runDnsRefresh() {
    ImmutableSet<VKey<Domain>> linkedDomainKeys =
        tm().transact(

The code gets a decent bit simpler if you don't combine basic error checking in the same transaction as loading all the linked domain keys -- thoughts on doing it that way? Then you shouldn't need this new exception class or special exception handling. And considering how infrequently this is called, having a single additional transaction is a fair trade-off for simpler code.