functionality of manual history cleaning by user proxy added (#1230)

* functionality of manual history cleaning by admin added

* formatting improved

* formatting improved 2

* formatting improved 3

* test function added

* test code formatting

* test code formatting 2

* more advanced logging. Now user can see nr of messages to preserve as confirmation

* test_invalid_allow_repeat_speaker uncommented

* warning when providing recepient agent and nr messages to preserve added, changed variables names

* code formatting

* code formatting

* code formatting

* added 'enable_clear_history' variable to GroupChat

* 'enable_clear_history' added, better descripted

* clearing groupchat history added

* clearing groupchat history added

* two ifs merged into one, formatting improved

* two ifs merged into one, formatting improved

* two ifs merged into one, formatting improved

* formatting

* formatting

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Co-authored-by: Davor Runje <davor@airt.ai>
Co-authored-by: Chi Wang <wang.chi@microsoft.com>