Set default connection pool size of RestClient to 80.

[ujjboy]

Motivation:

Set default connection pool size of RestClient to 80.

Modification:

• Set default connection pool size of RestClient to 80.
• Add multiple threads example of rest client.

Result:

Fixes #128 at 5.4.x

[codecov-io]

Codecov Report

Merging #129 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #129      +/-   ##
============================================
+ Coverage     65.33%   65.34%   +<.01%     
+ Complexity      657      656       -1     
============================================
  Files           272      272              
  Lines         11620    11620              
  Branches       1955     1955              
============================================
+ Hits           7592     7593       +1     
+ Misses         3065     3062       -3     
- Partials        963      965       +2

Impacted Files	Coverage Δ	Complexity Δ
...y/sofa/rpc/transport/rest/RestClientTransport.java	92.59% <100%> (ø)	4 <0> (ø)	⬇️
...pay/sofa/rpc/client/aft/InvocationStatFactory.java	82.92% <0%> (-4.88%)	15% <0%> (-1%)
...ent/aft/impl/ServiceHorizontalMeasureStrategy.java	84.44% <0%> (-2.23%)	26% <0%> (-1%)
...n/java/com/alipay/sofa/rpc/common/SofaConfigs.java	83.92% <0%> (-1.79%)	0% <0%> (ø)
...pay/sofa/rpc/transport/ClientTransportFactory.java	65.15% <0%> (+4.54%)	0% <0%> (ø)	⬇️
...m/alipay/sofa/rpc/module/FaultToleranceModule.java	93.33% <0%> (+26.66%)	5% <0%> (+1%)	⬆️

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