Feat: Add support for scoping jackett query with a `jackett_filter_index`

[disaac]

Currently nefarious performs searches with jackett using the all/results endpoint which searches all available indexers. In some cases there might be problematic indexers used for specific reasons that slow down or halt queries made by nefarious. Scoping queries to specific indexers would address this.

Issue Summary Unable to scope queries from nefarious to specific indexers in jackett

Proposed solution Jackett supports a filter-indexers endpoint allowing a search to be scoped to a set of indexers based on query parameters such as indexer tags. A setting could be added to the Jackett configuration nefarious_settings.jackett_filter_index allowing a query string to be set that overrides /all/ in jackett.py. By default if no value is set it will remain all

example before

return 'http://{}:{}/api/v2.0/indexers/all/results'.format(
        nefarious_settings.jackett_host, nefarious_settings.jackett_port)

after

return 'http://{}:{}/api/v2.0/indexers/{}/results'.format(
        nefarious_settings.jackett_host, 
        nefarious_settings.jackett_port,
        nefarious_settings.jackett_filter_index)

example nefarious_settings.jackett_filter_index value of !tag:appsonly+lang:en

The above would scope the query to only indexers that have a lang of english and no tag set as appsonly