[Form] Added a configuration that allow form extra data

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7209
| License       | MIT

I can not understand how https://github.com/symfony/symfony/commit/10998586787f31e5d1e33d4e21035c83cbe23489 can solve #7209 or #7229, so i created this PR.
I can not also understand why #7209 can be considered as duplicate of #1341 (https://github.com/symfony/symfony/commit/10998586787f31e5d1e33d4e21035c83cbe23489).

The commit https://github.com/symfony/symfony/commit/10998586787f31e5d1e33d4e21035c83cbe23489 will solve problem if some fields is missing, but says nothing about extra fields.