[fix][cli] Add get-cluster-migration cmd

[Technoboy-]

Motivation

#21359 forget to add get-cluster-migration cmd . And also make getClusterMigration async

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

[codecov-commenter]

Codecov Report

Merging #21473 (d19996c) into master (113d9f6) will increase coverage by 0.55%.
Report is 92 commits behind head on master.
The diff coverage is 53.33%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #21473      +/-   ##
============================================
+ Coverage     72.86%   73.42%   +0.55%     
- Complexity    32394    32674     +280     
============================================
  Files          1890     1893       +3     
  Lines        140401   140753     +352     
  Branches      15429    15503      +74     
============================================
+ Hits         102301   103344    +1043     
+ Misses        29987    29313     -674     
+ Partials       8113     8096      -17     

Flag	Coverage Δ
inttests	24.11% <0.00%> (-0.05%)	⬇️
systests	24.72% <0.00%> (-0.06%)	⬇️
unittests	72.70% <53.33%> (+0.56%)	⬆️

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

Files	Coverage Δ
.../java/org/apache/pulsar/admin/cli/CmdClusters.java	74.85% <100.00%> (+2.56%)	⬆️
.../apache/pulsar/broker/admin/impl/ClustersBase.java	80.26% <50.00%> (-0.15%)	⬇️

... and 204 files with indirect coverage changes