Add fuzzy env variable matching

[paullgdc]

Description

This PR replaces os.environ.get and os.getenv calls with a proxy object that checks if the env variable is not set wether another variable with a close name is set.

Checklist

• Add additional sections for feat and fix pull requests.
• Library documentation and/or Datadog's documentation site is updated. Link to doc PR in description.

Motivation

Design

Testing strategy

Relevant issue(s)

Testing strategy

Reviewer Checklist

• Title is accurate.
• Description motivates each change.
• No unnecessary changes were introduced in this PR.
• Avoid breaking API changes unless absolutely necessary.
• Tests provided or description of manual testing performed is included in the code or PR.
• Release note has been added for fixes and features, or else changelog/no-changelog label added.
• All relevant GitHub issues are correctly linked.
• Backports are identified and tagged with Mergifyio.

[mergify]

⚠️ The sha of the head commit of this PR conflicts with #4590. Mergify cannot evaluate rules on this PR. ⚠️