feat(client): add support for global retry configuration

[pablopalacios]

@redonkulus we were only able to set retry configuration per request. Now, it's possible to set some (or all) configuration globally:

const fetchr = new Fetchr({
    retry: {
     interval: 350,
     statusCodes: [0, 502, 504],
   },
});

fetchr.read('resource').clientConfig({ retry: { maxRetries: 2 } }).end();

This avoids repeating some configuration that (at least in our case) are always the same.

I confirm that this contribution is made under the terms of the license found in the root directory of this repository's source tree and that I have the authority necessary to make this contribution on behalf of its copyright owner.

[pablopalacios]

Soooo, @redonkulus , would it be possible to check this one?

[redonkulus]

I’m fine with a global config. Added one comment. We should document this in the readme too.

[redonkulus]

Why is called unsafe?

[pablopalacios]

the unsafeAllowRetry allows POST requests to be retried. In many cases, however, one would not like to have this feature enabled (since it could lead to duplicated transactions in the back-end). For me, a better name would be retryOnPost or something like this so it's clear what is happening (or, perhaps, removing this flag completely since, right now, retry is disabled by default).

Regarding the documentation, it's already in the readme:

fetchr/README.md

Line 477 in 081b3c7

**Note:** Fetchr doesn't retry POST requests for safety reasons. You can enable retries for POST requests by setting the `unsafeAllowRetry` property to `true`:

[konarkmodi]

@redonkulus @pablopalacios : Thanks to both of you for keeping this project alive and kicking. It's total bliss to use it.
Would it be possible to move this PR ahead and make the retry options globally available?

[redonkulus]

@konarkmodi thanks for the kind words. @pablopalacios do you want to update the readme, then we can get this merged?

[pablopalacios]

@redonkulus I thought it was already there. In any case, I updated the documentation to make it clearer (hopefully :D).

[redonkulus]

Thanks for the docs update, its clearer now.

[redonkulus]

https://github.com/yahoo/fetchr/releases/tag/v0.7.9