Implement naive feed configuration storage

[lthurston]

Description

This is the beginning of an idea to read / write feed configuration from / to the filesystem. This allows feeds to be tracked in the filesystem, like any other configuration or code. Developers will be able to create the feeds locally, write the feed to the filesystem using ./craft feed-me/feed-config-storage/write, commit that file, and, as a deploy step, read the configuration from disk with ./craft feed-me/feed-config-storage/read.

This hasn't been fully tested. I assume there are glaring bugs. Is this a feature that might be considered valuable enough to be incorporated into the plugin, or are we unique in this need? We can, but prefer not to, maintain our own fork, but I'd rather share this work with others.

I'm curious to hear your thoughts and whether you can offer any course corrections or other feedback. Thanks!

Note: you will need to mkdir config/feed-me for this to work at the moment.

[tricki]

FYI I manually extracted some feeds but ran into some problems when deploying to different servers with different databases. The main problem was the fact that the configuration contains auto-generated IDs (e.g. siteId), which might be different on different deployments. In my current solution I still have to configure those manually (site, section type and entry type, if I remember correctly).