fix: update Bidi-streaming guide to 1.19.0

[kazunori279]

fix: update Bidi-streaming guide to 1.19.0

[koverholt]

Chiming in on this PR since it's related to some CI build warning cleanup that I'm doing.

In #1023, I fixed a bunch of build warnings, but there is one remaining:

INFO    -  The following pages exist in the docs directory, but are not included in the "nav" configuration:
             - streaming/custom-streaming.md

As part of the bidi / streaming docs overhaul you've done, can streaming/custom-streaming.md be deleted from this repo now? Or should it be re-surfaced in the nav? Please feel free to delete or re-list it as needed, either in this PR or in #1021. Thanks!

[kazunori279]

Chiming in on this PR since it's related to some CI build warning cleanup that I'm doing.

In #1023, I fixed a bunch of build warnings, but there is one remaining:

INFO    -  The following pages exist in the docs directory, but are not included in the "nav" configuration:
             - streaming/custom-streaming.md

As part of the bidi / streaming docs overhaul you've done, can streaming/custom-streaming.md be deleted from this repo now? Or should it be re-surfaced in the nav? Please feel free to delete or re-list it as needed, either in this PR or in #1021. Thanks!

Yes, we'll delete it on another PR: #1021