[Request]: Make delimiter for artist mbids metadata configurable

[lyarenei]

Description

In some cases, an uncommon value delimiter can appear in metadata which can store multiple values. This causes issues with listen submission and fixing it requires updating a source code + releasing a new plugin version.

Proposed solution

Make delimiters configurable, so admins can configure it according to their metadata format. This will also eliminate the need of updating source code and making releases, so the fix is more immediate.

Additional context

#103
#109