Allow configuring of RSS feed read timeout

If an RSS feed is generated dynamically on demand by a dynamic backend, it can take more time than if it is just served from a static file.

In my specific case, the feed for an OsmCha.org filter is served within 7 seconds, thus it can't be followed:

> error Failed to create connection: Could not read feed from URL: timeout of 5000ms exceeded.

Start by locating the RSS feed-reading entry point and the current 5000ms timeout mentioned in the issue. Trace how feed settings are configured, then make the timeout configurable and verify that a feed taking about 7 seconds can be read when the setting permits it.

Written by the indexing model from the issue text.