Support custom header

[OrezzerO]

Motivation:

Add an api to add custom headers

[codecov]

Codecov Report

Merging #1050 (cb10a54) into master (03abf33) will decrease coverage by 0.14%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #1050      +/-   ##
============================================
- Coverage     68.84%   68.69%   -0.15%     
+ Complexity      820      817       -3     
============================================
  Files           407      408       +1     
  Lines         17619    17634      +15     
  Branches       2728     2729       +1     
============================================
- Hits          12130    12114      -16     
- Misses         4085     4113      +28     
- Partials       1404     1407       +3     

Impacted Files	Coverage Δ
...ay/sofa/rpc/filter/ConsumerCustomHeaderFilter.java	100.00% <100.00%> (ø)
...om/alipay/sofa/rpc/context/RpcInternalContext.java	83.76% <100.00%> (+0.87%)	⬆️
...java/com/alipay/sofa/rpc/module/LookoutModule.java	52.38% <0.00%> (-33.34%)	⬇️
...m/alipay/sofa/rpc/module/FaultToleranceModule.java	63.63% <0.00%> (-31.82%)	⬇️
...ipay/sofa/rpc/server/bolt/BoltServerProcessor.java	63.23% <0.00%> (-5.15%)	⬇️
...a/com/alipay/sofa/rpc/event/LookoutSubscriber.java	85.22% <0.00%> (-2.28%)	⬇️
...a/com/alipay/sofa/rpc/common/utils/ClassUtils.java	78.23% <0.00%> (-2.05%)	⬇️
.../main/java/com/alipay/sofa/rpc/event/EventBus.java	70.58% <0.00%> (-1.97%)	⬇️
...ipay/sofa/rpc/tracer/sofatracer/RpcSofaTracer.java	88.13% <0.00%> (-0.90%)	⬇️
...lipay/sofa/rpc/message/AbstractResponseFuture.java	56.14% <0.00%> (-0.88%)	⬇️
... and 1 more

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[EvenLjj]

LGTM