Rule: Prevent use of new GROUP syntax

[leeuwe]

In relation to the upcoming RF 7.2 release, I think there's a use case for a rule to prevent the use of the new GROUP syntax. Supported by this comment from Pekka: https://robotframework.slack.com/archives/C0K0240NL/p1735646205809349?thread_ts=1735603358.090759&cid=C0K0240NL

[bhirsz]

Sure. Though I believe it should be non-default rule (disabled by default, opt-in rule).

On the topic I was already thinking about possible rules for GROUP syntax - I will open some other issues as well.

[leeuwe]

I agree on the non-default. Thanks for the effort!