Bump fboss2 CLI nested-command MAX_DEPTH to 6

The routing-policy term match/action commands nest six levels deep
(config protocol bgp policy routing-policy term match), which trips
static_assert(N <= M) in utils::arrayToTuple via CmdArgsLists::getTypedArgs.
Raise CmdArgsLists::MAX_DEPTH from 5 to 6 to match.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: hillol-nexthop

fboss/cli/fboss2/CmdArgsLists.h

@@ -71,7 +71,7 @@ class CmdArgsLists {
  private:
   // since we do a lot of work of figuring out argument types at compile time,
   // for now we need to know the the theoretical max depth of nested subcommands
-  static constexpr auto MAX_DEPTH = 5;
+  static constexpr auto MAX_DEPTH = 6;
 
   std::array<std::vector<std::string>, MAX_DEPTH> data_;
 };