Add devcontainer.json to support .NET 9 samples in GitHub Codespaces … #811

Job	Run time
build (macos-latest, Release)	3m 0s
build (windows-latest, Debug)	9m 4s
build (macos-latest, Debug)	2m 4s
build (windows-latest, Release)	4m 39s
build (ubuntu-latest, Debug)	3m 58s
build (ubuntu-latest, Release)	4m 11s
publish-coverage	0s
	26m 56s

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