Move selenium service & configuration to compose.dev.yaml

[piotrkwiecinski]

selenium configuration sits in compose.yaml instead of compose.dev.yaml

Closes #867

[what-the-diff]

PR Summary

• Refined Instructions for Selenium Image Activation
  The instructions have been updated to mention the compose.yaml file instead of the previously mentioned compose.dev.yaml file. This is to enable the selenium image, a tool necessary for automating web browsers, providing flexibility in how automated tests are written and run.

• Improved extra_host value Updates
  The way in which extra_host values are updated has been enhanced. These values represent additional networks that the service wants to connect to, allowing for more efficient communication between different services.

[markshust]

I'm going to reopen this one as well -- the Selenium config should live in the compose.dev.yaml file.

[piotrkwiecinski]

This PR modifies documentation as currently selenium definition is located here https://github.com/markshust/docker-magento/blob/release/next/compose/compose.yaml#L138-L143

To my PR should be closed and code should be moved to compose.dev.yaml file instead.

[markshust]

Yup -- I'll add in an update that moves it over to compose.dev.yaml, and merge it in along with this doc update.