Start Development of NNStreamer 2.1.1 (2.2 RC2)

Start Development of NNStreamer 2.1.1 (2.2 RC2)

This is the version marking for 2.1.1 development start.
As 2.1.0 is started on Sep 28 2021, the change is huge.

2.1.0 -> 2.1.1
- Tizen 7.0 M1 RCx preparation and NNStreamer Mini Summit 2022-04 release.

- NNStreamer-Edge refactoring (module for Among-Device AI (a.k.a. Edge-AI))
        - Ongoing effort of nnstreamer-edge separation from nnstreamer.
        - In the future, nnstreamer-edge will provide among-device AI functions and nnstreamer will provide gstreamer plugins for such functions. Non-gstreamer systems may connect to nnstreamer-edge based pipelines without gstreamer as clients.
        - NNStreamer-Edge will be using AITT as its default backend, leaving protocol issues to AITT.
        - In the future, nnstreamer-edge will be compatible with non-Linux ultra-lightweight systems (e.g., Tizen-RT)

- ML-Service API preparation is going on at api.git.

- Major features
        - MQTT timestaamping w/ NTP. (later will be migrated to nnstreamer-edge & aitt)
        - Query (later will be migrated to nnstreamer-edge & aitt): robustness support, mqtt-hybrid protocol, performance fixes for multi-clients.
        - More coverage for SNPE support: quantized model support, SNPE dimension bug workaround, fixes from/for production team.
        - Flexible tensor support w/ decoder, converter, flatbuffer.

- Minor features
        - MQTT unittest basis, generic stream support, android support, timeout handling, ... (and many!)
        - Utility functions exported for plugin writers.
        - Tensorflow-lite delegation refactored for generality: may use XNNPACK more easily.
        - Tensorflow-lite multi-lib support.
        - PyTorch: support complex output tensor formats.
        - NNStreamer multi-lib support.
        - Decoder: boundingbox-yolov5
        - Filter: TRIx-Engine support. (NPUs of Samsung 2022 TV)
        - Docker support refactored and cleaned up.

- Fixes
        - ARMNN build errors.
        - Android errors
        - Build errors with recent compiler updates. (gcc 11)
        - Fixes upstreamed from productions
        - Errors w/ library updates: Lua >= 5.3, GLib >= 2.68
        - Regression fixes: openvino, edgetpu, tensorrt
        - Memory leaks in C++ subplugin infra.

- Known issues: PPA/Launchpad build broken!

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>