Spring Add web support for YAML via Jackson

Hello. This is my first spring framework contribution code.

I created this PR to add an application/yaml MediaType.

Recently, I noticed that application/yaml has been officially added to MediaType. The link I checked is below.

Link - https://www.rfc-editor.org/rfc/rfc9512.html - https://www.iana.org/assignments/media-types/media-types.xhtml

Thanks a lot.

Comment From: pivotal-cla

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Comment From: pivotal-cla

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Comment From: sdeleuze

Merged and polished, thanks for your contribution.

Comment From: ikaakkola

Hint for others wondering why their requests are suddenly using "application/yaml" instead of JSON - check if you are manually (re)creating MappingJackson2HttpMessageConverter and adding it to the end of a RestTemplates MessageConverters list.