Setup custom listing processors

[ahmedwalid05]

Hello there,
I am sending a draft of this PR to get early feedback. Happy to iterate as needed.

My end goal is to be able to configure Fredy to calculate the distance and travel time between a predefined address(es) and the listing address, and add this information to the notifications. The user should be able to configure all the required information for the Google Maps API (Or another API provider if implemented), the destination information and mode of transport through the UI.

This PR only includes setting up a "processor" construct. Processors are files that add info or transform the listings. I have only added a static processor for now, as a proof of concept. Will continue once/if the approach is accepted.

Remaining work before PR can be merged:

• Add Google map distance and travel time processor.
• Add distance & travel time to existing notifiers.
• Add UI for processors.
• Add tests for processors and update old tests for the new fredy runtime parameters.
• Update README, docs and architecture diagram.
• Update CONTRIBUTING guide to add a section for new processors.

Please let me know if I missed anything.

Not part of this PR:

Future improvements to this design could add a similarity check as a "filter" processor. i.e.:

[orangecoding]

Hey.

Sorry it took so long, I was on a business trip. In general, I like the idea :) What is your plan about processors in general, would you:

• let every processor run for every job?
• if so, some processors might be only needed for a very small fraction of Fredy's users (e.g. travel time), how do you make sure, it's opt in rather than on by default?
• I like the idea of having the similary check as a processor.

[ahmedwalid05]

Hi there,

To answer your questions, my plan was to let users configure it using the UI just like notifications.
Sadly, since this PR was started, I have gotten busy and just don't have time to continue working on this.
Please feel free to use any of my ideas/code.

Apologies!