Add a read option

[maxdanilov]

This PR is adding an option for fetching a value of a field from a project item without changing it, by setting the new operation field.

operation can be either read or update (update is the default one, preserving the current behavior of the action).

[maxdanilov]

@benbalter what do you think about this idea? I realized that with the recent change in #4, this option is very cheap to add.

[benbalter]

Thanks again @maxdanilov! 🎉

[benbalter]

@maxdanilov wanted to thank you for this PR. I actually needed to use this feature recently and was grateful it existed.