Add configuration options for net/http timeouts

[pkqk]

These timeouts should be tuneable for users who don't want to limit downstream services to only accept fast responses.

Address #228 by providing the option to increase the write timeout.

@codedge can you give this a review and see if it addresses your issue, it wasn't able to be configured by the limits plugin as it's the main method that sets up the http.Server instances.

In the config.json you can either provide a default-timeouts map of read, write and idle keys that will be used for all the http.Server instances or override the defaults with gateway-timeouts and private-timeouts maps that only need to provide values differing from the defaults.

[codecov-commenter]

Codecov Report

Attention: 23 lines in your changes are missing coverage. Please review.

Comparison is base (3c1b58b) 71.07% compared to head (71a4e80) 72.24%.

Files	Patch %	Lines
config.go	41.02%	14 Missing and 9 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #229 +/- ## ========================================== + Coverage 71.07% 72.24% +1.16% ========================================== Files 27 27 Lines 2742 2781 +39 ========================================== + Hits 1949 2009 +60 + Misses 671 631 -40 - Partials 122 141 +19 ```

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[codedge]

Going to check during the day and will let you know.

Thanks already for the fast response!

[codedge]

This works perfectly for me. 👍 Can be merged!