Refactor Developer Practices documentation

[erinysong]

Story

As a developer, I want to easily reference (and update as needed) development practices for our project, so I can follow best development practices and our project maintains consistent code quality.

Acceptance Criteria

• Update dev-practices folder to add docs for relevant engineering practices on .gov project. Think of what engineering practices would be useful to someone first onboarding onto .gov. Possible examples include (but may not necessarily): PR reviews, naming conventions, testing conventions, scripts, USWDS and front-end overrides.
• Remove outdated information in engineering standards docs (mainly thinking of Contributing.md and our scripts docs).
• Present updated dev-practices docs at engineering huddle for team review.

Additional Context

Engineering Huddle Notes
Engineering standards library - Our engineering practices are spread out across separate docs (PR review template, accessibility, contributing.md in our repo) that we can just put in one place. We can collect our engineering standards into one library/handbook, especially so people who onboard can more easily reference how to do things.

The idea is to have a living doc of engineering practices that cannot be inferred by just looking at our codebase.

Possible References

• cloud.gov dev-practices
• ACF data GitHub standards
• CCAO handbook coding standards

Issue Links

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