Release v0.8.0

[MrAlias]

This release upgrades its go.opentelemetry.io/otel dependency to v0.8.0, includes minor fixes, and new instrumentation.

Resolves #127

Additions

• Create this CHANGELOG.md. (Create a changelog to document changes between versions #114)
• Add emicklei/go-restful/v3 trace instrumentation. (Add emicklei/go-restful instrumentation #115)

Changed

• Update CONTRIBUTING.md to ask for updates to CHANGELOG.md with each pull request. (Create a changelog to document changes between versions #114)
• Move all github.com package instrumentation under a github.com directory. (Move all github.com instrumentation plugins down one level in directory hierarchy #118)

Fixed

• Update README to include information about external instrumentation.
  To start, this includes native instrumentation found in the go-redis/redis package. (Add link to go-redis/redis OpenTelemetry integration #117)
• Bump github.com/golangci/golangci-lint from 1.27.0 to 1.28.2 in /tools. (Bump github.com/golangci/golangci-lint from 1.27.0 to 1.28.0 in /tools #122, Bump github.com/golangci/golangci-lint from 1.28.0 to 1.28.1 in /tools #123, Bump github.com/golangci/golangci-lint from 1.28.1 to 1.28.2 in /tools #125)
• Bump go.mongodb.org/mongo-driver from 1.3.4 to 1.3.5 in /instrumentation/go.mongodb.org/mongo-driver. (Bump go.mongodb.org/mongo-driver from 1.3.4 to 1.3.5 in /instrumentation/go.mongodb.org/mongo-driver #124)