[#2362] Documentation for label_attr option in Form Compontent
Merge branch 'form-label-attr-documentation' of github.com:dorians/symfony-docs into dorians-form-label-attr-documentation

Conflicts:
	reference/forms/types/choice.rst
	reference/forms/types/collection.rst
	reference/forms/types/country.rst
	reference/forms/types/currency.rst
	reference/forms/types/email.rst
	reference/forms/types/entity.rst
	reference/forms/types/integer.rst
	reference/forms/types/language.rst
	reference/forms/types/locale.rst
	reference/forms/types/money.rst
	reference/forms/types/number.rst
	reference/forms/types/percent.rst
	reference/forms/types/text.rst
	reference/forms/types/timezone.rst
	reference/forms/types/url.rst