🎉 Added incremental indexer command

[pushrbx]

Currently none of the indexing artisan commands can do incremental indexing. So far we relied on the season and schedule indexer (or full indexing in reverse order), but in case of self-hosted setups that's insufficient, the new entries from MAL never get imported. Not to mention manga entries.
This PR adds a new artisan command: indexer:incremental. This command will compare the latest version of MAL ids from the mal_id_cache github repository and compares them with the downloaded ids from the previous run. If no ids found from the previous run, a full indexing session is started.

Usage:

php artisan indexer:incremental anime manga

The first argument is an array, and it's required. You can also just run it with one media type to index:

php artisan indexer:incremental anime

You can also resume with --resume flag if you cancelled it. The command handles the SIGTERM singal as well to gracefully stop.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 101 lines in your changes missing coverage. Please review.

Project coverage is 56.58%. Comparing base (744bd69) to head (3ec81f2).
Report is 12 commits behind head on master.

Files with missing lines	Patch %	Lines
...pp/Console/Commands/Indexer/IncrementalIndexer.php	0.00%	101 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #558      +/-   ##
============================================
- Coverage     57.86%   56.58%   -1.28%     
- Complexity     1361     1390      +29     
============================================
  Files           339      340       +1     
  Lines          5273     5625     +352     
============================================
+ Hits           3051     3183     +132     
- Misses         2222     2442     +220     

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