Make load_concerns a named initializer so Pro can schedule initializers before and after it.

[MSP-9653](https://jira.tor.rapid7.com/secure/RapidBoard.jspa?rapidView=84&view=detail&selectedIssue=MSP-9653)

Trying to schedule initializers in Pro to run after config/initializers/load_concerns caused a cycle in the initializers due to the initializer in pro having to say `after: :load_config_initializers' while other Pro initializers said `before: :load_config_initializers`.  By giving load_concerns the name 'metasploit_concern.load_concerns', it is possible to schedule initializers after it without causing a cycle as pro can refer to only its own config/initializers when it says `before: :load_config_initializers` now.