Add deprecation support in Swagger

[dunglas]

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Fixed tickets	n/a
License	MIT
Doc PR	todo

Follows #1962. Add the deprecated flag to operations that can be applied to deprecated resources:

namespace App\Entity;

use ApiPlatform\Core\Annotation\ApiProperty;
use ApiPlatform\Core\Annotation\ApiResource;

/**
 * @ApiResource(deprecationReason="This resource is deprecated")
 */
class DeprecatedResource
{
  // ...
}

Unfortunately, unlike GraphQL, Open API v2 doesn't support fields deprecation, or deprecation messages. Open API v3 supports fields deprecation, but API Platform don't have support for this version yet (help welcome)!