Add a deprecation warning about --link on default nw

[akerouanton]

Related to:

• daemon: add a deprecation warning about links on the default nw moby/moby#47427

- What I did

Update the "Deprecated Engine Features" doc page.

[codecov-commenter]

Codecov Report

Merging #4892 (ad19553) into master (f2e98f9) will increase coverage by 0.00%.
Report is 1 commits behind head on master.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4892   +/-   ##
=======================================
  Coverage   61.31%   61.32%           
=======================================
  Files         287      287           
  Lines       20063    20063           
=======================================
+ Hits        12301    12303    +2     
+ Misses       6868     6867    -1     
+ Partials      894      893    -1     

[robmry]

It's deprecated for the default bridge, so --network bridge too. Also, once the default bridge is a normal bridge network, I think --link will work but it'll do the same as it does for other bridges? So, it's the difference in behaviour that's deprecated, rather than the option, and it probably needs a more involved description?

Maybe something like ...

When used with the default bridge network, the --link option on docker create and docker run, creates Legacy Container Links. An entry for the linked container is added to the /etc/hosts file, and the linked container's Docker originated environment variables are exposed in the new container.

When used with any any other network, the --link option simply creates a DNS alias for the linked container.

The behaviour of Legacy Container Links is deprecated in v26.0. In a future release, --link will behave in the same way for all networks.

Note that the behaviour of the --link option is unchanged when a non-default network is used.

[thaJeztah]

I'm tempted to say that we deprecated it since docker 1.10 (when libnetwork was integrated in moby/moby#19198), but as we never added that to deprecated.md, perhaps instead we should add some crumble-path / references in the description below.

We can already fill in the Remove column though, at least if we plan to remove it in v28.0;

Deprecated: the feature is marked "deprecated" and should no longer be used. The feature may be removed, disabled, or change behavior in a future release. The "Deprecated" column contains the release in which the feature was marked deprecated, whereas the "Remove" column contains a tentative release in which the feature is to be removed. If no release is included in the "Remove" column, the release is yet to be decided on.