core: redo search cache from scratch. resolves #10382 (#10447)

In simple words, when you make a request in Jackett, the results are saved in memory (cache). The next request will return results form the cache improving response time and making fewer requests to the sites.
* We assume all indexers/sites are stateless, the same request return the same response. If you change the search term, categories or something in the query Jackett has to make a live request to the indexer.
* There are some situations when we don't want to use the cache:
** When we are testing the indexers => if query.IsTest results are not cached
** When the user updates the configuration of one indexer => We call CleanIndexerCache to remove cached results before testing the configuration
** When there is some error/exception in the indexer => The results are not cached so we can retry in the next request
* We want to limit the memory usage, so we try to remove elements from cache ASAP:
** Each indexer can have a maximum number of results in memory. If the limit is exceeded we remove old results
** Cached results expire after some time
* Users can configure the cache or even disable it

src/Jackett.Server/Controllers/ServerConfigurationController.cs

@@ -88,6 +88,9 @@ namespace Jackett.Server.Controllers
                     throw new Exception("The Base Path Override must start with a /");
             }
 
+            var cacheEnabled = config.cache_enabled;
+            var cacheTtl = config.cache_ttl;
+            var cacheMaxResultsPerIndexer = config.cache_max_results_per_indexer;
             var omdbApiKey = config.omdbkey;
             var omdbApiUrl = config.omdburl;
 
@@ -99,6 +102,10 @@ namespace Jackett.Server.Controllers
             serverConfig.UpdateDisabled = updateDisabled;
             serverConfig.UpdatePrerelease = preRelease;
             serverConfig.BasePathOverride = basePathOverride;
+            serverConfig.CacheEnabled = cacheEnabled;
+            serverConfig.CacheTtl = cacheTtl;
+            serverConfig.CacheMaxResultsPerIndexer = cacheMaxResultsPerIndexer;
+
             serverConfig.RuntimeSettings.BasePath = serverService.BasePath();
             configService.SaveConfig(serverConfig);