DX: Add setup guide for using VS Code Dev Containers

[abergs]

📔 Objective

I didn't know we had suport for dev containers and there were some setup steps that I stumbled upon and needed help to solve. I've documented what I think is the process, but I'm more than happy with edits.

Once this is merged we can also link to it from the contributing guidelines.

📸 Screenshots

⏰ Reminders before review

• Contributor guidelines followed
• All formatters and local linters executed and passed
• Written new unit and / or integration tests where applicable
• Protected functional changes with optionality (feature flags)
• Used internationalization (i18n) for all UI strings
• CI builds passed
• Communicated to DevOps any deployment requirements
• Updated any necessary documentation (Confluence, contributing docs) or informed the documentation team

🦮 Reviewer guidelines

• 👍 (:+1:) or similar for great changes
• 📝 (:memo:) or ℹ️ (:information_source:) for notes or general info
• ❓ (:question:) for questions
• 🤔 (:thinking:) or 💭 (:thought_balloon:) for more open inquiry that's not quite a confirmed issue and could potentially benefit from discussion
• 🎨 (:art:) for suggestions / improvements
• ❌ (:x:) or ⚠️ (:warning:) for more significant problems or concerns needing attention
• 🌱 (:seedling:) or ♻️ (:recycle:) for future improvements or indications of technical debt
• ⛏ (:pick:) for minor or nitpick changes

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.84%. Comparing base (ba57ca5) to head (c8b11c0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6318   +/-   ##
=======================================
  Coverage   49.84%   49.84%           
=======================================
  Files        1824     1824           
  Lines       80899    80899           
  Branches     7178     7178           
=======================================
  Hits        40328    40328           
  Misses      39015    39015           
  Partials     1556     1556           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[github-actions]

Checkmarx One – Scan Summary & Details – 871d28eb-7ade-4674-ab15-bd33cd74feaf

Great job! No new security vulnerabilities introduced in this pull request

[withinfocus]

bitwarden/contributing-docs#154 never got finished but we should get that done. The approach we've been using with documentation in repos is that the close-to-code content is about the component such as how it works and how an owning team would work on and maintain it; the contributing docs is for how to use it. This means that most of this content needs to show up in the other PR.