Adding a setup helper for attribute metadata config

[judahnator]

I noticed there was a \Doctrine\ORM\Tools\Setup::createAnnotationMetadataConfiguration method, but a method for attributes was missing. This PR adds a similar \Doctrine\ORM\Tools\Setup::createAttributeMetadataConfiguration method as well.

First time PR to Doctrine so go easy :)

[greg0ire]

This is a new feature and as such, should target 2.11.x. You can retarget with the Edit button.
Note that I'm not 100% sure about this, since it could also be seen as a bugfix for something we forgot. WDYT @SenseException @derrabus

[SenseException]

Technically 2.11, but Setup just exists to make things easier for users, so I guess 2.10 would be okay too.

[judahnator]

Where are we at with this one? Any last changes needing made?

[derrabus]

Any last changes needing made?

Yes, the CI needs to be green.

[derrabus]

Other than that, are we able to provide a test for your change?

[judahnator]

I wrote a test and the checks have passed!

[greg0ire]

There are 7 commits, please get rid of the first one, and squash the others together

How to do that?

1. git rebase -i origin/2,11,x, assuming origin is a git remote that points to this repository, and not your fork. If you're not sure what your remotes are, run git remote -vvv, there should be your fork and the holy/reference/base/origin/whatever-you-call-it repository.
2. A window will show up with many lines, replace pick with drop on the first line, and then pick with fixup on every line but the second one
3. Close your editor, git should do its magic, and you should end up with one commit
4. Use git push --force to overwrite what you already push. Don't forget the --force option otherwise git will try to merge both things together.

[judahnator]

Neat! I didn't know about those neat git tricks. Hopefully, I got everything right!

[greg0ire]

Congrats @judahnator !