contrib/gomodule/redigo: adds the DialURLContext method

[Succo]

Matches what the redigo package provides.
Also rewrite non context variant of dialer to use Context equivalent with context.Background

What does this PR do?

Matches what the redigo package provides.
Also rewrite non context variant of dialer to use Context equivalent with context.Background

Motivation

Matches what the redigo package provides is done so that DialURL can propagates the caller context.

Also rewrite non context variant of dialer to use Context equivalent with context.Background is done to reduce duplication in code and ensure switching to the Context aware variant has no side effect.

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.
• 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.
• For internal contributors, a matching PR should be created to the v2-dev branch and reviewed by @DataDog/apm-go.

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[darccio]

LGTM. Waiting on @DataDog/apm-idm-go approval.