Differentiate between role name and role key

[RafaelKr]

We're creating a role called Portal Customer. We'd like to use the role key portal_customer for that. Especially because for Symfony the role would be called ROLE_SULU_PORTAL CUSTOMER (note the space) without setting the key.

I'd like to create a PR, but we have the following options:

1. Create a new configuration key in config/packages/sulu_community.yaml with the path sulu_community.website.role_name corresponding to the role configuration option.

2. Create the PR to https://github.com/sulu/sulu and adjust the following line to replace spaces with underscores: https://github.com/sulu/sulu/blob/15a676466de29d815d016b37dd7cb97fef1cc76d/src/Sulu/Bundle/SecurityBundle/Entity/Role.php#L130. Of course this would be a breaking change so the PR would be against the 3.0 branch.
   Also the AsciiSlugger could be used which is available from Symfony 5.0, using _ as the seperator.

3. Doing both PRs

What is your preferred approach to that? Of course I'm open to other solutions too.

Edit: AsciiSlugger is available starting from Symfony 5.0, before I told it's available from 7.1 as that is what the version selector in the documentation suggested.