Emit deprecation warning on "enabled" attribute change

[cbuescher]

Starting in 7.0, we will throw an error if a user tries to change the "enabled" attribut in a mapping (#33933 (edited).
In addition to this we should emit a deprecation warning in 6.x, letting the user know that their intended enabled setting mapping change is silently ignored
(see #33566) and that we will start throwing errors on this with the next major version.

[elasticmachine]

Pinging @elastic/es-search-aggs

[cbuescher]

Closing since we decided to backport #33933 in the end.