impl(storage): make RestClient http transport the default

[scotthart]

Part of the work for #9659

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This change is 

[google-cloud-cpp-bot]

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Google Cloud Build Logs For commit: 24224e99dac75616aa965e153bb47f53bc7fa7c1

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[codecov[bot]]

Codecov Report

Merging #9680 (fc93776) into main (c2e6865) will decrease coverage by 0.46%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #9680      +/-   ##
==========================================
- Coverage   94.29%   93.83%   -0.47%     
==========================================
  Files        1494     1494              
  Lines      139060   139062       +2     
==========================================
- Hits       131124   130482     -642     
- Misses       7936     8580     +644     

Impacted Files	Coverage Δ
google/cloud/storage/client_options.cc	88.46% <100.00%> (+0.19%)	:arrow_up:
google/cloud/storage/client_options_test.cc	100.00% <100.00%> (ø)
google/cloud/storage/client_test.cc	98.60% <100.00%> (-0.02%)	:arrow_down:
google/cloud/storage/grpc_plugin_test.cc	100.00% <100.00%> (ø)
google/cloud/storage/internal/rest_client.cc	15.39% <0.00%> (-83.30%)	:arrow_down:
...ogle/cloud/storage/internal/rest_request_builder.h	79.16% <0.00%> (-20.84%)	:arrow_down:
google/cloud/internal/curl_impl.h	80.00% <0.00%> (-20.00%)	:arrow_down:
...oogle/cloud/storage/internal/sign_blob_requests.cc	88.88% <0.00%> (-11.12%)	:arrow_down:
google/cloud/storage/internal/hmac_key_requests.cc	93.93% <0.00%> (-6.07%)	:arrow_down:
...le/cloud/storage/internal/notification_requests.cc	94.73% <0.00%> (-5.27%)	:arrow_down:
... and 15 more

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[google-cloud-cpp-bot]

Google Cloud Build Logs For commit: d8805e4936fe832526c5c83e1b47bc1de81e39a9

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Google Cloud Build Logs For commit: 7ae875abc3dd2024730169cece99caece330486c

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Google Cloud Build Logs For commit: aff22ec09d974378b404309ffd9e8c188f9fc509

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Google Cloud Build Logs For commit: fc93776e4759f37067968d392d5ebd5902561e13

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