[improve][doc] Add specified_positions_divide split algorithm in doc

[Demogorgon314]

Motivation

#13796 added specified_positions_divide split algorithm, but some docs are missing.

Documentation

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[Demogorgon314]

/pulsarbot run-failure-checks

[Demogorgon314]

/pulsarbot run-failure-checks

[dave2wave]

/pulsarbot run-failure-checks

[github-actions[bot]]

The pr had no activity for 30 days, mark with Stale label.

[codecov-commenter]

Codecov Report

Merging #16293 (40dfa70) into master (1b5722d) will increase coverage by 1.51%. The diff coverage is 90.00%.

@@             Coverage Diff              @@
##             master   #16293      +/-   ##
============================================
+ Coverage     46.34%   47.86%   +1.51%     
- Complexity    10394    10672     +278     
============================================
  Files           703      703              
  Lines         68838    68845       +7     
  Branches       7379     7382       +3     
============================================
+ Hits          31905    32953    +1048     
+ Misses        33324    32195    -1129     
- Partials       3609     3697      +88     

Flag	Coverage Δ
unittests	47.86% <90.00%> (+1.51%)	:arrow_up:

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

Impacted Files	Coverage Δ
...ookkeeper/mledger/impl/ManagedCursorContainer.java	76.80% <85.71%> (+0.76%)	:arrow_up:
...r/service/AbstractDispatcherMultipleConsumers.java	48.38% <100.00%> (+2.62%)	:arrow_up:
...ava/org/apache/pulsar/broker/service/Consumer.java	71.35% <100.00%> (+2.31%)	:arrow_up:
...lsar/broker/loadbalance/impl/ThresholdShedder.java	3.27% <0.00%> (-27.87%)	:arrow_down:
...ker/loadbalance/impl/LeastLongTermMessageRate.java	73.33% <0.00%> (-20.00%)	:arrow_down:
...rg/apache/pulsar/broker/lookup/v1/TopicLookup.java	60.00% <0.00%> (-13.34%)	:arrow_down:
...org/apache/pulsar/broker/loadbalance/LoadData.java	58.33% <0.00%> (-8.34%)	:arrow_down:
...roker/loadbalance/impl/ModularLoadManagerImpl.java	59.39% <0.00%> (-4.87%)	:arrow_down:
...a/org/apache/pulsar/client/impl/RawReaderImpl.java	83.90% <0.00%> (-1.15%)	:arrow_down:
...rg/apache/pulsar/proxy/server/ProxyConnection.java	55.21% <0.00%> (-1.13%)	:arrow_down:
... and 65 more

[tisonkun]

Merging...

Thanks for taking care of this!