* [plugin/route53]: Support batch mode operation.

Cache all Route53 records internally using `ListResourceRecordPagesWithContext`
and serve them from memory.

Bonus features:

  * Support additional r53 record types (`CNAME`, `SOA`, etc)
  * Support `upstream` option (#2099 filed to support argument optionality)
Signed-off-by: Dmitry Ilyevskiy <dmitry.ilyevskiy@getcruise.com>
Signed-off-by: Dmitry Ilyevskiy <ilyevsky@gmail.com>