[From] missing options in EntityType

[HeahDude]

Hi there,

Since 2.7, options introduced by symfony/symfony#14050 are inherited by EntityType and works well except choice_value which failed at validation step but will be fix by symfony/symfony#17694. However not all of them are mentioned in the doc.

There were recent PR for choice_translation_domain and translation_domain, as of 2.7 EntityType is still missing some doc for choice_value, choice_attr, and choice_name.

I'm sending a PR for this.