Local Custom Definitions

[kushfest]

Is your feature request related to a problem? Please describe.
There are an unknowable number of private indexers with strict policies that prohibit them from being added to the indexer server. At present there is no way to locally add them to Prowlarr. A custom yml file added to the Definitions folder appears to be ignored and only the indexers from the indexer server are displayed as options in the Add Indexer modal.

Describe the solution you'd like
Add the ability for local yml files in the Definitions folder to be loaded for use in Prowlarr. These should be denoted in the UI as local for easy reference and to be clear that they will not auto-update.