Linter + Small refactor

[didil]

• Fixes #35
• Added golangci-lint linter
• Refactored http command options to a new package level HttpCmdOpts struct to reduce the number of package level variables (removing package level variables would require a bigger refactor to change the way the cobra commands are initialised, not a priority for now)

[jimaek]

This wont affect/break the release scripts, right? https://github.com/jsdelivr/globalping-cli/tree/master/.github/workflows

[didil]

@jimaek it shouldn't affect the release scripts. Is there a way to test the release scripts apart from triggering a release ?

[jimaek]

Probably not, I guess we will just have to try and release at some point to see if it breaks.