Support grpc connection pooling

[congqixia]

See also #637

[sre-ci-robot]

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[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 43 lines in your changes are missing coverage. Please review.

Project coverage is 73.95%. Comparing base (43226a3) to head (d7e7849).
Report is 15 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #638      +/-   ##
==========================================
- Coverage   74.95%   73.95%   -1.00%     
==========================================
  Files          44       44              
  Lines        4125     4293     +168     
==========================================
+ Hits         3092     3175      +83     
- Misses        921      990      +69     
- Partials      112      128      +16     

Files	Coverage Δ
client/alias.go	100.00% <100.00%> (ø)
client/authentication.go	100.00% <100.00%> (ø)
client/config.go	74.19% <100.00%> (+2.76%)	⬆️
client/mq_message.go	90.90% <100.00%> (-9.10%)	⬇️
client/rbac.go	100.00% <100.00%> (ø)
client/resource_group.go	100.00% <100.00%> (ø)
client/row.go	85.77% <100.00%> (-0.65%)	⬇️
client/client.go	37.20% <83.33%> (+8.26%)	⬆️
client/maintainance.go	87.75% <92.85%> (-7.60%)	⬇️
client/partition.go	86.88% <96.96%> (+2.81%)	⬆️
... and 7 more

[congqixia]

/kind feature

[congqixia]

/hold