Add metadata property to `DependencyGraph.CreateSnapshot`

[eyalk007]

Hi,
I wanted to ask when would support for metadata property be available for the CreateSnapshot function?
currently it is only supported using the api😕

[gmlewis]

This would be a great PR for any new contributor to this repo or a new Go developer.
All contributions are greatly appreciated!

Feel free to volunteer for any issue and the issue can be assigned to you so that others don't attempt to duplicate the work.
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Please check out our CONTRIBUTING.md guide to get started. (In particular, please remember to go generate ./... and don't use force-push to your PRs.)

Thank you!

[eyalk007]

#3640
opened a pull request here 😁