[feat][admin] Add offload managedLedgerOffloadThreshold RestAPI and CLI tools

[tjiuming]

Motivation

Add offload managedLedgerOffloadThreshold RestAPI and CLI tools

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• Anything that affects deployment

Documentation

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

Matching PR in forked repository

PR in forked repository: tjiuming#8

[codecov-commenter]

Codecov Report

❌ Patch coverage is 76.19048% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.26%. Comparing base (aeb4503) to head (77b8032).
⚠️ Report is 3301 commits behind head on master.

Files with missing lines	Patch %	Lines
.../org/apache/pulsar/broker/admin/v2/Namespaces.java	71.42%	5 Missing and 1 partial ⚠️
...pache/pulsar/broker/admin/impl/NamespacesBase.java	80.95%	4 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #18218       +/-   ##
=============================================
+ Coverage     31.39%   47.26%   +15.86%     
- Complexity     6651    10465     +3814     
=============================================
  Files           697      697               
  Lines         68015    68058       +43     
  Branches       7285     7286        +1     
=============================================
+ Hits          21353    32166    +10813     
+ Misses        43667    32311    -11356     
- Partials       2995     3581      +586     

Flag	Coverage Δ
unittests	47.26% <76.19%> (+15.86%)	⬆️

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

Files with missing lines	Coverage Δ
...pache/pulsar/broker/admin/impl/NamespacesBase.java	64.13% <80.95%> (+51.94%)	⬆️
.../org/apache/pulsar/broker/admin/v2/Namespaces.java	59.74% <71.42%> (+50.40%)	⬆️

... and 171 files with indirect coverage changes

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[tjiuming]

/pulsarbot run-failure-checks