Add system.filesystem.limit as an opt-in metric

[mx-psi]

Name	Description	Units	Instrument Type	Value Type	Attribute Key	Attribute Values
system.filesystem.limit	Total memory available in the disk.	By	UpDownCounter	Int64	device	(identifier)
					state	used, free, reserved
					type	ext4, tmpfs, etc.
					mode	rw, ro, etc.
					mountpoint	(path)