api: return more replication info

[xhebox]

Signed-off-by: xhe xw897002528@gmail.com

What problem does this PR solve?

Previously, only a boolean value is returned to indicate whether it is scheduled. But there are a lot of cases, when pd can not really make the schedule and waiting for something. A typical example is you ask for more replications than there is. And this requirement origins from pingcap/tidb#30960.

Close #4509

What is changed and how it works?

Now it returns a three-valued string.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has HTTP API interfaces change (Don't forget to add the declarative for API)

Release note

return three-valued state string for regions replication check api

[ti-chi-bot]

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[codecov]

Codecov Report

Merging #4508 (ad2195f) into master (24bf11d) will increase coverage by 0.03%.
The diff coverage is 70.00%.

@@            Coverage Diff             @@
##           master    #4508      +/-   ##
==========================================
+ Coverage   74.91%   74.95%   +0.03%     
==========================================
  Files         265      265              
  Lines       27844    27851       +7     
==========================================
+ Hits        20860    20875      +15     
+ Misses       5121     5114       -7     
+ Partials     1863     1862       -1     

Flag	Coverage Δ
unittests	74.95% <70.00%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
server/api/region.go	67.59% <66.66%> (-0.28%)	⬇️
server/cluster/coordinator.go	75.15% <100.00%> (+0.05%)	⬆️
server/tso/global_allocator.go	61.90% <0.00%> (-4.77%)	⬇️
server/member/member.go	64.70% <0.00%> (-2.14%)	⬇️
pkg/btree/btree.go	85.78% <0.00%> (-0.97%)	⬇️
server/grpc_service.go	51.40% <0.00%> (-0.58%)	⬇️
server/server.go	71.49% <0.00%> (-0.30%)	⬇️
server/cluster/cluster.go	82.96% <0.00%> (+0.34%)	⬆️
server/tso/tso.go	65.34% <0.00%> (+0.56%)	⬆️
tools/pd-ctl/pdctl/command/hot_command.go	71.32% <0.00%> (+0.69%)	⬆️
... and 5 more

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[nolouch]

/merge

[ti-chi-bot]

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/run-all-tests

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: ad2195f