Spring Modify status code 103 to ("Early Hints")

According to rfc8297(https://tools.ietf.org/html/rfc8297), the reason phase of status code 103 should be "Early Hints", not "Checkpoint".

This commit modifies the status code 103 reason phase from ("Checkpoint") to ("Early Hints").

Comment From: waisink

Thank you for replying and suggesting.

However i am wondering that if preserve the old constants, is that ok when use old constants value to call the method HttpStatus.valueOf as the following expression return false

HttpStatus.CHECKPOINT.equals(HttpStatus.valueOf(HttpStatus.CHECKPOINT.value()))

Comment From: simonbasle

@waisink I implemented a change with the same goal as yours but going down the deprecation road in #29816, with an additional method to compare arbitrary status codes' value