dev: format src/oas.md

[ralfhandl]

Part of

• Create dev build infrastructure #4223

New npm script format-markdown formats src/oas.md.

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[baywet]

@ralfhandl to re-target to dev instead of main

[handrews]

@ralfhandl does this mean that the published markdown will be different from the markdown in github? If so, wouldn't it be better to make format-markdown a precommit hook instead?

[ralfhandl]

This script allows ad-hoc formatting of src/oad.md, that is the file that will eventually be released to main.

It is the same script that we used to format 3.1.1.md and 3.0.4.md in their respective dev branches before releasing them to main.

We can later additionally automate this.