Add build-time support for customizable default API and URL endpoints

[kyparisisg]

Description: This update allows the use of build-time values to customize the default API and URL endpoints.

Usage: You can override the default endpoints during the build process by using the following -ldflags options during go build:

-ldflags "-X main.defaultAPI=https://your-custom-api.com -X main.defaultURL=https://your-custom-url.com"

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 71.76%. Comparing base (044f411) to head (ad95f75). Report is 3 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2513 +/- ## ========================================== + Coverage 69.65% 71.76% +2.11% ========================================== Files 8 8 Lines 669 673 +4 ========================================== + Hits 466 483 +17 + Misses 172 158 -14 - Partials 31 32 +1 ```

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