Update Action to use new ProjectsV2 api

[lukewar]

Currently beta ProjectNext API is going to be deprecated soon. Is is being replaced with new ProjectV2 API.

In this PR I am updating add-to-project action to use new ProjectV2 API.

[lukewar]

I have update the Readme and removed reference from @main branch in the examples since we make releases now. I have also removed the section How to point the action to a specific branch or commit sha for the same reason.

@mattcosta7 WDYT about making 0.1.0 release when merge those changes?

[mattcosta7]

@lukewar @ekroon - conflicts on the built output, after landing a few updates here.

When are we planning to push this one forward?

[ekroon]

@lukewar @ekroon - conflicts on the built output, after landing a few updates here.

When are we planning to push this one forward?

We have removed the feature flag for the new API yesterday, so we can move forward with this now.

[Mattamorphic]

We updated the addProjectV2ItemById mutation to return a item field instead of projectItem to align with other call sites across the ProjectV2 mutations and objects.

[lukewar]

Tested recent changes 💯.

Last action's failure is expected because I have changed the scope to insufficient level.

[mattcosta7]

Are the docs here still correct - or can they be updated as well to account for the new project scoped tokens?

https://github.com/actions/add-to-project#inputs

specifically around the scopes necessary for this token

[lukewar]

Are the docs here still correct - or can they be updated as well to account for the new project scoped tokens?

https://github.com/actions/add-to-project#inputs

specifically around the scopes necessary for this token

Thanks for asking. It was updated, but your comment made me double check and it wasn't updated in all places. 🙇