cluster: restart prometheus after scaling the cluster

[AstroProfundis]

What problem does this PR solve?

The prometheus config is not reloaded correctly after scaling in a cluster.

What is changed and how it works?

Restart the prometheus instance after updating configs, otherwise new configs are not applied.

Check List

Tests

• Integration test

Code changes

• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity

Related changes

• Need to cherry-pick to the release branch

Release notes:

NONE

[lonng]

LGTM

[lonng]

/merge

[ti-srebot]

Your auto merge job has been accepted, waiting for:

• 695
• 707

[codecov-commenter]

Codecov Report

Merging #717 into master will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #717      +/-   ##
==========================================
+ Coverage   57.93%   57.97%   +0.03%     
==========================================
  Files         253      253              
  Lines       18522    18530       +8     
==========================================
+ Hits        10731    10743      +12     
+ Misses       6367     6365       -2     
+ Partials     1424     1422       -2     

Flag	Coverage Δ
#coverage	57.97% <ø> (+0.03%)	⬆️

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

Impacted Files	Coverage Δ
...c/github.com/pingcap/tiup/pkg/cluster/api/dmapi.go	62.77% <0.00%> (ø)
...src/github.com/pingcap/tiup/pkg/cluster/manager.go	69.00% <0.00%> (+0.15%)	⬆️
...com/pingcap/tiup/components/dm/command/scale_in.go	69.41% <0.00%> (+0.36%)	⬆️
...ingcap/tiup/components/cluster/command/scale_in.go	82.35% <0.00%> (+0.53%)	⬆️
...c/github.com/pingcap/tiup/pkg/cluster/api/pdapi.go	57.01% <0.00%> (+1.21%)	⬆️

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[ti-srebot]

/run-all-tests

[ti-srebot]

@AstroProfundis merge failed.