update changelog for 0.4.0 release #174

Job	Run time
astropy unit tests	10m 24s
gwcs unit tests	1m 7s
jwst unit tests	42m 11s
specutils unit tests	2m 21s
weldx unit tests	2m 33s
sunpy unit tests	3m 23s
dkist unit tests	4m 0s
asdf-astropy unit tests	3m 25s
asdf-standard unit tests	57s
asdf-transform-schemas unit tests	1m 18s
asdf-wcs-schemas unit tests	1m 29s
asdf-coordinates-schemas unit tests	3m 17s
	1h 16m 25s

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