EQL: Deprecate wildcard function

[astefan]

Since there's now a dedicated syntax using like / like~ / regex / regex~, we should deprecate the wildcard function.
It should be considered deprecated in a later 7.x release and drop completely from 8.0.

[elasticmachine]

Pinging @elastic/es-docs (Team:Docs)

[elasticmachine]

Pinging @elastic/es-ql (Team:QL)

[astefan]

@jrodewig can you, please, have a look at this one? Many thanks.