Opentelemetry Req - v0.2.0

Changes

• opentelemetry_req: Don't assume request.headers shape @wojtekmach (#193)
• Revert span name change to pre-1.18 spec @bryannaegele (#214)
• Relax Req's elixir version @bryannaegele (#196)
• opentelemetry_req: Don't assume request.options is a map @wojtekmach (#192)
• Add source_url_pattern to enable linking to source @sPatrik (#168)
• Improve Req with OTel http spec @rlopzc (#163)