Enable fedach and fedwire download from proxy

[burnettekm]

frbservices.org is not always available when we need to download the fedach or fedwire data. The ability to get this data from a proxy or cache instead of frbservices.org would be very helpful.

This PR enables Fed to fetch data from a custom URL(i.e. private service or NGINX). The custom URL must be set in the CUSTOM_DOWNLOAD_URL environment variable. The custom URL must include the formatting directive %s where %s is the listName. This value is interpolated into the URL at the time the request is made.

Ex: "https://frbservices.org/EPaymentsDirectory/directories/%s?format=json"

If this environment variable is not supplied, Fed defaults to the url in the above example.

[codecov-commenter]

Codecov Report

Merging #268 (92c717a) into master (d4d3022) will increase coverage by 3.02%.
The diff coverage is 60.00%.

❗ Current head 92c717a differs from pull request most recent head 32b3082. Consider uploading reports for the commit 32b3082 to get more accurate results

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #268      +/-   ##
==========================================
+ Coverage   65.61%   68.64%   +3.02%     
==========================================
  Files          16       16              
  Lines         922      928       +6     
==========================================
+ Hits          605      637      +32     
+ Misses        295      261      -34     
- Partials       22       30       +8     

[adamdecaf]

Do you want to try building this image yourself make docker locally and verifying it works in platform-dev before we merge?

[burnettekm]

Do you want to try building this image yourself make docker locally and verifying it works in platform-dev before we merge?

Yes, I'll give it a shot. Thanks for the idea.