[Continuous Batching] Changes in notify_handle() + simple metrics reporting

[mzegla]

Changes:

• switching operation order in notify_handle, so that generation status is set before sending out last token, so user will never get status RUNNING when generation is already done and no new tokens will come
• add simple metrics giving some basic information about pipeline state like number of all requests, number of running request, cache usage etc.

[ilya-lavrenov]

build_jenkins