* Add v3 equivalents of v2 configs that were included in v3 due to no
  transitive deprecation. This increases consistency and reduces user
  confusion. We will continue to support these straggler v2 configs
  beyond the v2 turndown due to the late addition of v3 counterparts,
  special case code is added to utility.cc to handle this.

* There were two extensions, //envoy/config/cluster/redis and
  //envoy/config/retry/previous_priorities, that for some reason were
  not upgraded to use v3 config. This is now fixed and I've grepped for
  other v2 in //source, none remain.

Risk level: Medium (changes to extension config types and deprecated
  config handling).
Testing: Additional unit test added for utility.cc handling, upgraded
  configs to v3 for other tests.

Fixes envoyproxy#14735
Fixes envoyproxy#12841

Signed-off-by: Harvey Tuch <htuch@google.com>
Co-authored-by: Abhay Narayan Katare <abhay.katare@india.nec.com>

Signed-off-by: Harvey Tuch <htuch@google.com>

Signed-off-by: Harvey Tuch <htuch@google.com>