What does this PR do?

Fixes contrib/gorilla/mux so it enforces go1.18, since it is injecting generics through the github.com/DataDog/dd-trace-go/v2/instrumentation/options package.

This issue has arised in one of the Orchestrion benchmarks that instruments traefik, which has a replace of gorilla/mux pointing to a fork of an old version that does not have a go.mod: https://github.com/traefik/traefik/blob/master/go.mod#L394

Additionally, updates the aspect to use the v2 instrumentation api instead of using internal packages.

Motivation

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• New code is free of linting errors. You can check this by running golangci-lint run locally.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

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