Introduce `asdf.util.load_yaml` #2393

Job	Run time
asdf / Load tox environments	5s
astropy / Load tox environments	5s
stsci / Load tox environments	7s
third-party / Load tox environments	7s
asdf / asdf-wcs-schemas (ubuntu-latest)	1m 17s
asdf / asdf-coordinates-schemas (ubuntu-latest)	2m 1s
astropy / asdf-astropy (ubuntu-latest)	2m 33s
astropy / specutils (ubuntu-latest)	1m 42s
stsci / gwcs (ubuntu-latest)	1m 6s
stsci / jwst (ubuntu-latest)	19m 12s
stsci / stdatamodels (ubuntu-latest)	2m 52s
stsci / stpipe (ubuntu-latest)	40s
stsci / roman_datamodels (ubuntu-latest)	1m 14s
third-party / weldx (ubuntu-latest)	2m 38s
third-party / sunpy (ubuntu-latest)	2m 12s
third-party / dkist (ubuntu-latest)	2m 53s
	40m 44s

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