JcrRemotingServlet should use 'application/json' media type for JSON response

When retrieving a JCR node using JSON binding like the following by appending '.json' to the path, the content-type of the response should have been application/json, instead of the current text/plain;charset=utf-8.

GET http://localhost:8080/server/default/jcr:root/hello.json

Reproduction:

• Create a node (e.g, hello) like the following (excerpt from [1]):

  $ curl --request MKCOL --data @- --user name:pass \
         http://localhost:8080/server/default/jcr:root/hello/ <<END
  <sv:node sv:name="hello" xmlns:sv="http://www.jcp.org/jcr/sv/1.0">
    <sv:property sv:name="message" sv:type="String">
      <sv:value>Hello, World!</sv:value>
    </sv:property>
    <sv:property sv:name="date" sv:type="Date">
      <sv:value>2022-01-15T12:00:00.000Z</sv:value>
    </sv:property>
  </sv:node>
  END
  

• Retrieve the node by JSON binding:

  $ curl -i --user admin:admin http://localhost:8080/server/default/jcr:root/hello.json
  

• The Content-Type response header should be "application/json" or one of its compatibles.
  But the actual value is "text/plain;charset=utf-8".

[1] https://jukkaz.wordpress.com/2009/11/24/jackrabbit-over-http/