Support obtaining ServerWebExchange in ContextView

[JohnNiang]

What type of PR is this?

/kind feature
/area core
/milestone 2.20.x

What this PR does / why we need it:

This PR registers a ServerWebExchangeContextFilter to make ServerWebExchange available under ContextView. The usage example is as follows:

Mono.deferContextual(contextView -> {
    var exchange = ServerWebExchangeContextFilter.getExchange(contextView);
    assertTrue(exchange.isPresent());
    return mono;
})

Does this PR introduce a user-facing change?

None

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.18%. Comparing base (6cd8dc8) to head (c421aae).
Report is 87 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##               main    #6705     +/-   ##
===========================================
  Coverage     58.18%   58.18%             
- Complexity     3774     3945    +171     
===========================================
  Files           651      679     +28     
  Lines         22125    23217   +1092     
  Branches       1538     1582     +44     
===========================================
+ Hits          12873    13509    +636     
- Misses         8641     9084    +443     
- Partials        611      624     +13     

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[ruibaby]

/lgtm

[f2c-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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