Improvements on Thymeleaf reactive configuration

[danielfernandez]

Thymeleaf 3.0.8 (see #10319) added two new configuration parameters to ThymeleafReactiveViewResolver:

• fullModeViewNames
• chunkedModeViewNames

When a maximum chunk size is specified (in Spring Boot: spring.thymeleaf.reactive.max-chunk-size) these two new parameters allow to optionally fine-tune specifically which templates will be applied the specified maximum chunk size (and thus be executed in CHUNKED mode) and which won't.

See thymeleaf/thymeleaf-spring#159 for a detailed description of this new behaviour.

This PR modifies ThymeleafProperties and ThymeleafAutoConfiguration to add the possibility to configure these two new properties from the Spring Boot configuration mechanism. A couple of tests have been added too.

Additionally, there are two more commits included in the PR which perform a slight improvement in the doc of ThymeleafProperties and add a test for the spring.thymeleaf.reactive.max-chunk-size configuration property.

[danielfernandez]

Rebased and git push -f-ed branch after base code moved to spring-boot-project folder.

[bclozel]

Thanks @danielfernandez !