Fix some issues with large request bodies

[LucasPickering]

Description

Describe the change. If there is an associated issue, please include the issue link (e.g. "Closes #xxx"). For UI changes, please also include screenshots.

• Don't log request bodies
• Optimize TemplatePreview initialization to remove recursion. This fixes a stack overflow for large bodies
• Don't store request bodies >1MB in the DB
• Default to WARN log level

This is a first step toward #356

Known Risks

What issues could potentially go wrong with this change? Is it a breaking change? What have you done to mitigate any potential risks?

• Losing request data
• There's still perf issues with large bodies

QA

How did you test this?

Manual testing

Checklist

• Have you read CONTRIBUTING.md already?
• Did you update CHANGELOG.md?
  • Only user-facing changes belong in the changelog. Internal changes such as refactors should only be included if they'll impact users, e.g. via performance improvement.
• Did you remove all TODOs?
  • If there are unresolved issues, please open a follow-on issue and link to it in a comment so future work can be tracked