feat: Add folder upload support to dcc.Upload component #648

Job	Run time
Detect Relevant Path Changes	7s
Build Dash Package	3m 10s
Typing Tests	2m 48s
Table Server Tests (Group ${{ matrix.test-group }})	-1s
Table Unit/Lint Tests (Python ${{ matrix.python-version }})	-1s
Run Background & Async Callback Tests (Python ${{ matrix.python-version }})	-1s
	6m 2s

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