Resolve "ENG Create Side Nav component - Solutions"

• I, the Assignee, have run Axe Devtools on any updated pages, and fixed the relevant accessibility issues.
• These changes meet a specific OKR or item in our Quarterly Plan.
• These changes work on both Safari and Chrome.
• These changes have been reviewed for Visual Quality Assurance and Functional Quality Assurance on Mobile, Desktop, and Tablet.
• These changes work with our Google Analytics and SEO tools.
• These changes have been documented as expected.
• Images are appropriately sized

Added side navigation to source code management page, refactored scrolling to be more stable. I would like feedback on the styling and the scrolling interaction.

Review app: https://654-eng-create-side-nav-component-solutions-2.about.gitlab-review.app/stages-devops-lifecycle/source-code-management/

Closes #654 (closed)