Fix tests and adds support for custom schema

[at-silva]

feat(api): adds support for custom schema

• Adds support for custom schema i.e.:

  type (
      Config struct {
    	  Path string `schema:"{'required': true, 'starts_with': '/'}"`
      }
  )
  

fix(test): typo and coroutine deadlock

• Fixes #163

[CLAassistant]

All committers have signed the CLA.

[gszr]

I like the annotations usage to describe richer schemas. Thanks for opening this. We will look into this feature as soon as we can. I am downgrading this one to "draft" until we can approach this -- also taking requests like https://github.com/Kong/go-pdk/issues/93 into consideration.