refactor: pass in config as dependency instead of self initializing

What does this merge request do and why?

In !1590 (merged), we introduced the region field to the Snowplow context. It is currently resolved by directly instantiating Config. It was noted in !1590 (comment 2205752321) that this has an undesirable side effect (ie. reading .env file).

This MR addresses the suggestion in !1590 (comment 2205904796) to refactor the code so that config is passed in as a dependency argument.

Resolves #739 (closed).

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.