Improve RouterFunctions reference documentation [SPR-17016]

[spring-projects-issues]

Arjen Poutsma opened SPR-17016 and commented

With the implementation of #21491, we should improve the reference documentation for HandlerFunctions to use RouterFunctions.route().

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Issue Links:

• Create DSL for RouterFunction and RouterFunctions [SPR-16953] #21491 Create DSL for RouterFunction and RouterFunctions

Referenced from: commits fedbb09