[5111] Added "command-processed" hook point to BaseCommandMgr

[5111] Added "command-processed" hook point to BaseCommandMgr

src/lib/config/base_command_mgr.cc
 - BaseCommandMgr::BaseCommandMgr() - registers command-processed hookpoint
 - BaseCommandMgr::processCommand() - invokes command-processed callouts

src/lib/config/tests/command_mgr_unittests.cc
  - Cleanup and renaming to avoid confusion
  - Added new tests to verify hookpoint callout
      TEST_F(CommandMgrTest, commandProcessedHook)
      TEST_F(CommandMgrTest, commandProcessedHookReplaceResponse)