[Feature] Support the estimated number of ShuffleServers required.

[leixm]

What changes were proposed in this pull request?

Estimated number of ShuffleServers required.

Why are the changes needed?

Avoid manually specifying the number of ShuffleServers to improve user experience.

Does this PR introduce any user-facing change?

Yes.

How was this patch tested?

UT.

[codecov-commenter]

Codecov Report

Merging #322 (b00c2d9) into master (84f781f) will increase coverage by 0.16%.
The diff coverage is 85.71%.

@@             Coverage Diff              @@
##             master     #322      +/-   ##
============================================
+ Coverage     61.01%   61.17%   +0.16%     
- Complexity     1489     1503      +14     
============================================
  Files           185      185              
  Lines          9314     9356      +42     
  Branches        900      908       +8     
============================================
+ Hits           5683     5724      +41     
  Misses         3326     3326              
- Partials        305      306       +1     

Impacted Files	Coverage Δ
.../java/org/apache/hadoop/mapreduce/RssMRConfig.java	23.07% <ø> (ø)
...apache/hadoop/mapreduce/v2/app/RssMRAppMaster.java	0.00% <0.00%> (ø)
...rg/apache/uniffle/client/util/RssClientConfig.java	0.00% <ø> (ø)
...java/org/apache/uniffle/common/util/Constants.java	0.00% <0.00%> (ø)
...org/apache/spark/shuffle/RssSparkShuffleUtils.java	57.14% <85.71%> (+2.59%)	⬆️
...n/java/org/apache/hadoop/mapreduce/RssMRUtils.java	44.00% <100.00%> (+12.29%)	⬆️
.../java/org/apache/spark/shuffle/RssSparkConfig.java	93.61% <100.00%> (+0.13%)	⬆️
...ffle/common/segment/LocalOrderSegmentSplitter.java	90.62% <0.00%> (+2.38%)	⬆️
...che/uniffle/client/impl/ShuffleReadClientImpl.java	90.09% <0.00%> (+2.72%)	⬆️

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[jerqi]

LGTM, @zuston Do you have other suggestion?

[zuston]

LGTM, @zuston Do you have other suggestion?

Let me take a look.

[zuston]

LGTM

[zuston]

Merged. Thanks @leixm @jerqi .