Add external_id to WorkflowStepView

[srajiang]

Summary

Fixes #1391 by adding external_id properties required by views.update method.

Requirements (place an x in each [ ])

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[filmaj]

Hmm, now that I'm reviewing this, I'm wondering if these changes are correct. @seratch @srajiang can you double-check my assumptions below?

In digging into where these types are used, I can see that it is consumed in the @slack/web-api package: the super-type View is imported in src/methods.ts, a e.g. ViewsUpdateArguments interface uses the View as a view property and finally the e.g. views.update method uses ViewsUpdateArguments as the arguments to be passed in.

However, the optional external_id and view_id properties are set as properties on this ViewsUpdateArguments interface inside @slack/web-api - not on the WorkflowStepView type exported by @slack/types.

With that context, perhaps this isn't the right change? It seems like the various *View types exported by @slack/types are meant to model the view object to be passed into the various views.* API methods.

Perhaps there is nothing wrong here? Am I totally off-base?

[filmaj]

Nevermind! @srajiang and @bkeung astutely pointed out that the View object itself can also have the IDs as part of the responses coming back. My mistake!

[srajiang]

I have removed view_id from the type for now as Fil's pointed out view_id is set at the ViewsUpdateArguments and is not listed in the general views documentation.

[seratch]

Thanks for working on this! Not having view_id this time is fine, but we updated the view object in API response, not the API argument list here. As long as the actual payload has view_id, there is no reason not to have it. We may improve the incomplete views document page plus add the property too in the future.