Fix Document AI processing and obtaining results.

[denispeplin]

Both "process" and "batch process" are fixed, also operation retrivement is fixed. The location is hardcoded for now and set to US.

I'm not sure how to properly implement the location, especially in the Connection module. While for the functions I could add an extra parameter or an option, for the connection I don't see a standard way for doing so.

Any ideas?

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[denispeplin]

@googlebot I signed it!