feat: add "Becoming a Maintainer" course

[adiati98]

Description

This PR adds the "Becoming a Maintainer" course with following changes:

• Added a becoming-a-maintainer folder in the docs directory.
• Moved the course's files from maintainer course repo to the becoming-a-maintainer folder.
• Fixed links and adjusted wording to accomodate both courses.
• Moved .nojekyll file into the root of docs.
• Changed styling for accessibility purpose as shown in the screenshots. Color palettes are following OpenSauced's brand.

Related Tickets & Documents

Closes #169 #171

Mobile & Desktop Screenshots/Recordings

Before

After

Screen Recording

https://github.com/open-sauced/intro/assets/45172775/30bbb77c-a84b-4651-8e74-862cd9df3ef8

Steps to QA

Tier (staff will fill in)

• [ ] Tier 1
• [ ] Tier 2
• [ ] Tier 3
• [ ] Tier 4

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[BekahHW]

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