Modify offset range tracker to use first response as start offset

[kennknowles]

Update Python SDK to match #515

Imported from Jira BEAM-497. Original Jira may contain additional context.
Reported by: chamikara.

[mohamedawnallah]

.take-issue

[mohamedawnallah]

Freeing up my assignment to this good-first-issue so other contributors can jump in if interested! If no one picks it up by then, I'm happy to submit a PR to close it out

[mohamedawnallah]

.free-issue