feat(pubsub): per-call options in SchemaAdminClient

[coryan]

Part of the work #7689

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[google-cloud-cpp-bot]

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[codecov]

Codecov Report

Merging #8406 (c189c2a) into main (5837957) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #8406   +/-   ##
=======================================
  Coverage   95.04%   95.05%           
=======================================
  Files        1358     1359    +1     
  Lines      121163   121191   +28     
=======================================
+ Hits       115162   115195   +33     
+ Misses       6001     5996    -5     

Impacted Files	Coverage Δ
google/cloud/pubsub/schema_admin_client.cc	100.00% <100.00%> (ø)
google/cloud/pubsub/schema_admin_client_test.cc	100.00% <100.00%> (ø)
google/cloud/pubsub/schema_admin_connection.cc	95.91% <100.00%> (+6.12%)	⬆️
google/cloud/pubsub/schema_admin_connection.h	100.00% <100.00%> (ø)
google/cloud/pubsub/subscriber_connection_test.cc	97.22% <0.00%> (-0.70%)	⬇️
.../cloud/storage/benchmarks/throughput_experiment.cc	74.37% <0.00%> (-0.51%)	⬇️
...le/cloud/internal/default_completion_queue_impl.cc	97.72% <0.00%> (+0.56%)	⬆️

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[coryan]

@devbww please let me know if this is the pattern I should follow for the other *Client classes in Pub/Sub