deprecate the rename greylist field in state_point encoding and rename it to reconnect

The following discussion from !1934 (merged) should be addressed:

• @arvidnl started a discussion: (+1 comment)

  I think it seems slightly dangerous to have the deprecation strategy in a separate MR, we would be likely to forget about it. Do we have any ideas on how to proceed on the deprecation? Should it be something in style of "keep both fields for a certain number of releases, then remove the old one"?

Apart from this specific case, it's important to define a clear deprecation policy for encodings as this is going to be a common use case as the software evolves.