add attribute rules

[LordSimal]

This makes sure that something like this is not allowed:

#[DataProvider('irregularCreateTableProvider')] public function mymethod(): void

This also forces attribtues to be added bellow the docblock

Refs: cakephp/migrations#736

[LordSimal]

Don't know if we want other rules from https://github.com/slevomat/coding-standard/blob/master/doc/attributes.md#slevomatcodingstandardattributesattributesorder- in here as well

[markstory]

I think these make sense. The ordering and sniffs seem like rules that won't come up that often as we don't use attributes in the framework yet.