feat(spanner): add support for CMMR phase 2

[devbww]

Tests and samples for user-managed instance configurations.

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Here is the summary of changes.

You are about to add 4 region tags.

• google/cloud/spanner/samples/samples.cc:109, tag spanner_create_instance_config
• google/cloud/spanner/samples/samples.cc:156, tag spanner_update_instance_config
• google/cloud/spanner/samples/samples.cc:189, tag spanner_delete_instance_config
• google/cloud/spanner/samples/samples.cc:210, tag spanner_list_instance_config_operations

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For commit: 7d758772a168282e5c754364be348e9547b85182

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[codecov]

Codecov Report

Base: 94.24% // Head: 94.17% // Decreases project coverage by -0.06% ⚠️

Coverage data is based on head (7d75877) compared to base (4bb4dec).
Patch coverage: 27.27% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9872      +/-   ##
==========================================
- Coverage   94.24%   94.17%   -0.07%     
==========================================
  Files        1495     1495              
  Lines      139838   139981     +143     
==========================================
+ Hits       131787   131824      +37     
- Misses       8051     8157     +106     

Impacted Files	Coverage Δ
google/cloud/spanner/samples/samples.cc	62.86% <12.72%> (-2.25%)	⬇️
...ogle/cloud/spanner/testing/pick_instance_config.cc	78.94% <50.00%> (-3.41%)	⬇️
...e/cloud/spanner/testing/cleanup_stale_instances.cc	73.84% <75.86%> (+1.62%)	⬆️
...ogle/cloud/spanner/testing/random_instance_name.cc	100.00% <100.00%> (ø)
...integration_tests/schema_admin_integration_test.cc	98.88% <0.00%> (-1.12%)	⬇️
...cloud/pubsub/internal/subscription_session_test.cc	97.82% <0.00%> (-0.68%)	⬇️
...le/cloud/storage/internal/curl_download_request.cc	89.29% <0.00%> (+1.00%)	⬆️

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[coryan]

I am Okay with this, but curious about the rationale. Seems like an opportunity for flakes that we do not need?

[devbww]

Yes, I agree. At the moment I am only duplicating the behavior of CleanupStaleInstances(), which I didn't originate, but I will more than happily followup by removing both cases. Thanks.