docs(gax): include streaming APIs

[dbolduc]

Part of the work for #1468

Paginator will (hopefully soon) pick up a fn to_stream() which is gated by the unstable-stream feature. We want this to appear in our docs.

While client crates currently have an unstable-stream feature which is gating their stream() methods, and preventing the methods from appearing in our docs, we plan to change the method to paginator() and make it always available. (Hence there are no changes to client crates).

See: https://docs.rs/about/metadata

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Aside: Remind me where I can look at the generated documentation to make sure this change actually works...

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.95%. Comparing base (e5d7b72) to head (d6c69db).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1487   +/-   ##
=======================================
  Coverage   95.95%   95.95%           
=======================================
  Files          38       38           
  Lines        1531     1531           
=======================================
  Hits         1469     1469           
  Misses         62       62           

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[coryan]

Maybe it should be called _unstable-sdk-client...

[dbolduc]

Ack, not for this PR.