Symfony Uid support for Json schema

[norkunas]

Description

Since Symfony 5.1 the Uid component was introduced and when relying only on it instead of ramsey/uuid,
wrong schema is generated, because it detects it as an object instead of string:uuid.
There is a pull request to symfony for Uid normalizer https://github.com/symfony/symfony/pull/36406/files,
but there are two missing pieces:

• symfony/uid identifier normalizer;
• json schema to support uuid/ulid;

I can open separate PR's for both of these, but we should decide if the second point is a bugfix or a new feature?

Example
none

[soyuka]

You can add both to a single PR as these need symfony 5.1 anyway, thanks @norkunas !