[AclOrch] move ACL counters to flex counter infrastructure (sonic-net…

…#1943)

* [FlexCounterManager] Add ACL_COUNTER FC type
What I did
Added ACL Flex Counter group. Re-implemented ACL counters implemention to work with Flex Counter Infrastructure.
Why I did it
To improve orchagent performance when large amount of ACL rules are configured.
How I verified it
Together with depends PRs. Run ACL/Everflow test suite.
Signed-off-by: Stepan Blyschak <stepanb@nvidia.com>