Refactored Slack image with svg icon in "Getting Started" Page

[agutiernc]

Fixes #5830

What changes did you make?

• Replaced the slack image icon with an svg file icon on steps 2, 4, and 5
• Modified CSS to align the icon and make responsive

Why did you make the changes (we will use this info to test)?

• To update icon in svg format
• To reduce redundancy in code on the getting started page
• Make it simpler to change out the icon for a newer icon

Screenshots of Proposed Changes Of The Website

Visuals before changes are applied

Visuals after changes are applied

[github-actions]

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From your project repository, check out a new branch and test the changes.

git checkout -b agutiernc-refactor-getting-started-slack-icon-5830 gh-pages
git pull https://github.com/agutiernc/website.git refactor-getting-started-slack-icon-5830

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https://github.com/agutiernc/website/blob/refactor-getting-started-slack-icon-5830/CONTRIBUTING.md  

[agutiernc]

Ignore this pull request. Need to resolve a git issue. Will create a new pull request later.