Clarify the deprecation and removing strategies

[Jacques Le Roux <ja...@les7arts.com>]

Hi,

We already clarified things for services: https://markmail.org/message/ohzbubwacoyp6gpf

While working on OFBIZ-12168 "Rename some connoted words like blacklist and whitelist."

I found these:

 1. Three "Deprecated since branch release: Upcoming branch" in datamodel files
 2. One  "Update service for Deprecate since: branch release" in migration groovy files. I added another by copying :/
 3. Three  "Upcoming branch" (once removed point 1). 1 of these 3 is in DATAMODEL_CHANGES.adoc

I guess we agree that the same pattern used for services can be used for other things like entities, fields of entities or documentation.
It has been used by https://github.com/apache/ofbiz-framework/commit/44c374a/
So points 1 and 3 are not a problem

But it can't be applied to the second point where a service is not replaced but used to migrate data from an entity to another.
So it's impossible to use the "deprecated since" pattern and it's not of the Release Manager responsibility.

I suggest rather put a date there. It will allow to decide when to remove these services from time to time. I propose something like "Update service 
created 2021-02".
Done at https://github.com/apache/ofbiz-framework/commit/a608fa4b562bd9ea484785c0b1cde3f9305c8539/

Jacques