[ISSUE #3773] WebClientPlugin switched exchange() to retrieve() method

[spicydev]

Make sure that:

• [x] You have read the contribution guidelines.
• [ ] You submit test cases (unit or integration tests) that back your changes.
• [x] Your local test passed ./mvnw clean install -Dmaven.javadoc.skip=true.

[codecov-commenter]

Codecov Report

Merging #3776 (040a7b8) into master (04142f4) will decrease coverage by 0.00%. The diff coverage is 40.00%.

@@             Coverage Diff              @@
##             master    #3776      +/-   ##
============================================
- Coverage     64.23%   64.22%   -0.01%     
+ Complexity     6039     6038       -1     
============================================
  Files           900      900              
  Lines         24673    24677       +4     
  Branches       2237     2237              
============================================
+ Hits          15849    15850       +1     
- Misses         7425     7429       +4     
+ Partials       1399     1398       -1     

Impacted Files	Coverage Δ
...ache/shenyu/plugin/httpclient/WebClientPlugin.java	61.90% <40.00%> (-38.10%)	:arrow_down:
...henyu/plugin/grpc/resolver/ShenyuNameResolver.java	63.82% <0.00%> (+1.06%)	:arrow_up:
...ruptor/RegisterClientServerDisruptorPublisher.java	64.70% <0.00%> (+11.76%)	:arrow_up:
...controller/ShenyuClientHttpRegistryController.java	100.00% <0.00%> (+22.22%)	:arrow_up:

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[moremind]

maybe use exchangeToMono or exchageToFlux

[loongs-zhang]

@spicydev ci/cd failed, please check https://github.com/apache/shenyu/runs/7596239922?check_suite_focus=true

[loongs-zhang]

please update changes from master.

[loongs-zhang]

see https://github.com/apache/shenyu/pull/3792 ,sorry, please try another task @spicydev