Create configuration property to enable/disable HiddenHttpMethodFilter with WebFlux

[spencergibb]

Quoting @rstoyanchev

HiddenHttpMethodFilter is for use with browsers, and having it on by default in WebFlux where the body isn't automatically parsed is debatable I think. So perhaps a Boot ticket is worth creating still.

See spring-cloud/spring-cloud-gateway#541 (comment) for the discussion and workaround.

[spencergibb]

See also https://jira.spring.io/browse/SPR-17291

[bclozel]

It was introduced in gh-14008 - @rstoyanchev makes a good argument about that. It would still require us to disable that by default after enabling it in 2.0.5, and this would also be at odds with the current Spring MVC auto-configuration.

[bclozel]

We've discussed this and we think we should remain consistent here and register it still, because that's what we're doing for Spring MVC.

Let's turn this issue into an enhancement and add property that enables/disables this filter, since we've got the equivalent for Spring MVC with spring.mvc.hiddenmethod.filter.enabled.