Update interactive-mode example of adding an Arcade subscription

[dagood]

To double check:

• The right tests are in and and the right validation has happened. Guidance: https://github.com/dotnet/core-eng/tree/master/Documentation/Validation

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Updating Documentation/DependencyFlowOnboarding.md after going through it:

• With the standard Merge Policy, the Maestro++ PR check said Maestro auto-merge - Not implemented merge policy 'standard'. Changing to Standard (like other subscriptions I see) then closing the PR and triggering a new one seems to have fixed that.

• I noticed Pull Request Failure Notification Tags: '' now shows up in interactive mode, but isn't in the doc. It's fairly obvious what it does, and I left it blank, but I figured the example might as well include it.

The non-interactive example appears to do something different--not sure if it's more correct or less correct than interactive. 😄 I'd personally consider removing one of the options to simplify the doc (and its maintenance).

/cc @riarenas @MattGal

[riarenas]

Thanks Davis!

[MattGal]

Good catch!