Add support for doctrine/persistence v2

[nenadalm]

this is required to support php8: #2999

[stof]

Please also update the composer.json file to add a a conflict rule for doctrine/persistence < 1.3 as the new namespace is only available in 1.3+

[nenadalm]

done. I thought that I should update composer.lock too, but composer validate told me that it is out of sync anyway before I added the change, so I didn't touch it.

[acrobat]

@stof can we get this merged/released together with #3006 so libraries/applications depending on fos/user-bundle can move on with version compatibility support (php, doctrine etc)