ctl: add a message if the scheduler does not exist

[HuSharp]

What problem does this PR solve?

Issue Number: Ref #4399

What is changed and how does it work?

before

./pd-ctl scheduler config evict-leader-scheduler  add-store 2
Failed! [404] 404 page not found

After

./pd-ctl scheduler config evict-leader-scheduler  add-store  2
Failed! scheduler evict-leader-scheduler not found.

Check List

Tests

• Unit test

Release note

ctl: add a message if the scheduler does not exist

[HuSharp]

@okJiang PTAL, thx!

[codecov]

Codecov Report

Attention: Patch coverage is 69.23077% with 4 lines in your changes missing coverage. Please review.

Project coverage is 77.64%. Comparing base (3abbd72) to head (fb8a2a3).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8503      +/-   ##
==========================================
+ Coverage   77.60%   77.64%   +0.03%     
==========================================
  Files         474      474              
  Lines       61852    61864      +12     
==========================================
+ Hits        48003    48036      +33     
+ Misses      10317    10295      -22     
- Partials     3532     3533       +1     

Flag	Coverage Δ
unittests	77.64% <69.23%> (+0.03%)	⬆️

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

[okJiang]

Please add an issue for this pr

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-07 09:46:54.508111192 +0000 UTC m=+431744.375210281: ☑️ agreed by lhy1024.
• 2024-09-06 06:29:42.822729465 +0000 UTC m=+598707.340782387: ☑️ agreed by rleungx.

[rleungx]

/hold

[rleungx]

Let's wait for @okJiang to approve.

[HuSharp]

After discussing with PM. He gives suggestions for these 2 issues:

ask: what will error msg be like?

PM: The failed msg is Unable to update config: schedulerXX does not exist.

ask: Also, I noticed there are 2 ways for evictLeader and grantLeader:

1. ./pd-ctl scheduler add evict-leader-scheduler <store-id>
   If there is no evict leader scheduler before, no error will be reported and the scheduler for this store will be generated
2. ./pd-ctl scheduler config evict-leader-scheduler add-store <store_id>
   If there is no evict leader scheduler before, it will report the error: Failed! [404] 404 page not found

PM: Since add and config are two subcommands, it doesn't seem necessary to unify them, which makes sense.

cc @songrijie @okJiang @rleungx

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lhy1024, okJiang, rleungx

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• OWNERS [lhy1024,rleungx]

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[HuSharp]

/unhold