[DLStreamer] New DLS sample for usage of valve element in DLS pipeline.

[jmotow]

New DLStreamer sample to show how to use valve element in DLS pipeline.

[github-actions]

Remaining comments which cannot be posted as a review comment to avoid GitHub Rate Limit

pylint

libraries/dl-streamer/samples/gstreamer/python/open_close_valve/open_close_valve_sample.py|183 col 19| C0123: Use isinstance() rather than type() for a typecheck. (unidiomatic-typecheck)
libraries/dl-streamer/samples/gstreamer/python/open_close_valve/open_close_valve_sample.py|157 col 39| W0613: Unused argument 'pad' (unused-argument)
libraries/dl-streamer/samples/gstreamer/python/open_close_valve/open_close_valve_sample.py|157 col 50| W0613: Unused argument 'u_data' (unused-argument)
libraries/dl-streamer/samples/gstreamer/python/open_close_valve/open_close_valve_sample.py|234| C0116: Missing function or method docstring (missing-function-docstring)
libraries/dl-streamer/samples/gstreamer/python/open_close_valve/open_close_valve_sample.py|243| C0116: Missing function or method docstring (missing-function-docstring)
libraries/dl-streamer/samples/gstreamer/python/open_close_valve/open_close_valve_sample.py|285 col 11| W0718: Catching too general exception Exception (broad-exception-caught)
libraries/dl-streamer/samples/gstreamer/python/open_close_valve/open_close_valve_sample.py|280 col 26| W1309: Using an f-string that does not have any interpolated variables (f-string-without-interpolation)
libraries/dl-streamer/samples/gstreamer/python/open_close_valve/open_close_valve_sample.py|243| R1710: Either all return statements in a function should return an expression, or none of them should. (inconsistent-return-statements)
libraries/dl-streamer/samples/gstreamer/python/open_close_valve/open_close_valve_sample.py|274 col 20| W0612: Unused variable 'err' (unused-variable)
libraries/dl-streamer/samples/gstreamer/python/open_close_valve/open_close_valve_sample.py|10| C0411: standard import "sys" should be placed before third party imports "gi", "gi.repository.Gst" (wrong-import-order)
libraries/dl-streamer/samples/gstreamer/python/open_close_valve/open_close_valve_sample.py|11| C0411: standard import "sys" should be placed before third party imports "gi", "gi.repository.Gst" (wrong-import-order)
libraries/dl-streamer/samples/gstreamer/python/open_close_valve/open_close_valve_sample.py|12| C0411: standard import "time" should be placed before third party imports "gi", "gi.repository.Gst" (wrong-import-order)
libraries/dl-streamer/samples/gstreamer/python/open_close_valve/open_close_valve_sample.py|13| C0411: standard import "contextlib.contextmanager" should be placed before third party imports "gi", "gi.repository.Gst" (wrong-import-order)
libraries/dl-streamer/samples/gstreamer/python/open_close_valve/open_close_valve_sample.py|13| W0611: Unused contextmanager imported from contextlib (unused-import)