fix: configure context in async retries

[dbolduc]

Capture the current options in creation of the class. (I will consider accepting Options in the constructor instead, but I would rather get the fix out first). I will need to do the same thing for the async polling loop. There may be others...

In practice this change only affects bigtable, which uses GrpcSetupOption to preserve legacy behavior of bigtable::RPC*Policy::Setup(grpc::ClientContext&)

---

This change is 

[google-cloud-cpp-bot]

Google Cloud Build Logs
For commit: 6b67315b65a17168a2aa3d5ff6bc1f037650066c

• Public Access Build Logs
• Cloud Build Console (requires auth)
• Kokoro Logs (requires auth)

ℹ️ NOTE: Kokoro logs are linked from "Details" below.

[codecov]

Codecov Report

Base: 94.01% // Head: 94.02% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (6b67315) compared to base (ece8a56).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #10100   +/-   ##
=======================================
  Coverage   94.01%   94.02%           
=======================================
  Files        1513     1513           
  Lines      139621   139621           
=======================================
+ Hits       131268   131275    +7     
+ Misses       8353     8346    -7     

Impacted Files	Coverage Δ
google/cloud/internal/async_retry_loop.h	100.00% <100.00%> (ø)
google/cloud/internal/async_retry_loop_test.cc	99.41% <100.00%> (+<0.01%)	⬆️
...integration_tests/schema_admin_integration_test.cc	98.88% <0.00%> (-1.12%)	⬇️
google/cloud/pubsub/samples/samples.cc	90.77% <0.00%> (+0.07%)	⬆️
...cloud/pubsub/internal/subscription_session_test.cc	98.15% <0.00%> (+0.16%)	⬆️
google/cloud/completion_queue_test.cc	97.32% <0.00%> (+0.19%)	⬆️
google/cloud/storage/parallel_upload.cc	98.62% <0.00%> (+0.34%)	⬆️
...le/cloud/storage/internal/curl_download_request.cc	89.29% <0.00%> (+1.00%)	⬆️
...e/cloud/pubsublite/internal/alarm_registry_impl.cc	100.00% <0.00%> (+2.94%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.