Remove Spring dependency from Core

[whiskeysierra]

Detailed Description

The core should be made independent from Spring.

Context

We use primarily the ClientHttpRequest and ClientHttpRequestFactory abstractions together with HttpHeaders, HttpStatus and HttpSeries. Getting rid of Spring as a core dependency would potentially allow Riptide to be used in environments other than Spring.

Possible Implementation

• New module riptide-api (package org.zalando.riptide)
• riptide-core, re-package to org.zalando.riptide.core
• Most modules should depend exclusively on riptide-api
• The following modules should be the only ones with a Spring dependency
  • riptide-compatibility
  • riptide-spring-boot-autoconfigure
  • riptide-spring-boot-starter

Your Environment

• Version used: 3.x