Add Amazon Linux 2 to the install page

Porting gitlab-com/www-gitlab-com!100790 (closed) to the new repository.

• Updates wording regarding availability of arm64 packages to clarify that they will be automatically picked and users need not do anything.
• Adds support for pre-install notes and commands to list out things users might need to do before running the installation command
• Add Amazon Linux 2 to the install apge

Checklist

• 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