Allow passing PSR-3 loggers to setLogger as they are compatible

[Seldaek]

IMO you should really just use PSR-3 and require psr/log as it is anyway part of almost every PHP project at this point.. but at least this allows setting things up without getting static analysis warnings.

[CLAassistant]

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[dcr-stripe]

Thank you for the contribution @Seldaek and sorry about the delay! I'll discuss this with the team and get back to you but I think this makes a ton of sense!

[dcr-stripe]

Hi @Seldaek - this looks good to me! I've brought your branch up to head - there's a small linter error:

     /**
-     * @param Util\LoggerInterface|\Psr\Log\LoggerInterface $logger the logger to which the library
+     * @param \Psr\Log\LoggerInterface|Util\LoggerInterface $logger the logger to which the library
      *   will produce messages
      */

Do you mind applying this change, and then I can give this an approval and merge?

Thank you for the contribution!

[Seldaek]

Sure, done.